LED lighting systems and method

ABSTRACT

Embodiments of the invention include LED lighting systems and methods. For example, in some embodiments, an LED lighting system is included. The LED lighting system can include a flexible layered circuit structure that can include a top thermally conductive layer, a middle electrically insulating layer, a bottom thermally conductive layer, and a plurality of light emitting diodes mounted on the top layer. The LED lighting system can further include a housing substrate and a mounting structure. The mounting structure can be configured to suspend the layered circuit structure above the housing substrate with an air gap disposed in between the bottom thermally conductive layer of the flexible layered circuit structure and the housing substrate. The distance between the layered circuit structure and the support layer can be at least about 0.5 mm. Other embodiments are also included herein.

This application is a continuation-in-part of U.S. application Ser. No.13/592,090, filed Aug. 22, 2012, which is a continuation-in-part of U.S.application Ser. No. 13/158,149, filed Jun. 10, 2011, now U.S. Pat. No.8,851,356, which is a continuation-in-part of U.S. application Ser. No.12/372,499, filed Feb. 17, 2009, now U.S. Pat. No. 7,980,863, whichclaims the benefit of U.S. Provisional Application No. 61/028,779, filedFeb. 14, 2008, and U.S. Provisional Application No. 61/037,595, filed onMar. 18, 2008, the contents of all of which are herein incorporated byreference.

U.S. application Ser. No. 13/592,090 is also a continuation-in-part ofU.S. application Ser. No. 13/190,639, filed Jul. 26, 2011, now U.S. Pat.No. 8,500,456, which is a continuation of U.S. application Ser. No.12/406,761, filed Mar. 18, 2009, now U.S. Pat. No. 8,007,286, whichclaims the benefit of U.S. Provisional Application No. 61/037,595, filedon Mar. 18, 2008, and U.S. Provisional Application No. 61/043,006, filedApr. 7, 2008, the contents of all of which are herein incorporated byreference.

U.S. application Ser. No. 13/592,090 is also a continuation-in-part ofU.S. application Ser. No. 13/411,322, filed Mar. 2, 2012, now U.S. Pat.No. 8,525,193, which is a continuation of U.S. application Ser. No.12/043,424, filed Mar. 6, 2008, now U.S. Pat. No. 8,143,631, thecontents of all of which are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to light emitting diode (LED) lightingsystem and methods.

BACKGROUND OF THE INVENTION

Solid state lighting (SSL) circuits (or LED lighting systems) arepredicted to achieve widespread adoption in commercial lightingapplications. Solid state lighting is more efficient in convertingelectricity to light than incandescent, fluorescent, and compactfluorescent systems. As such solid state lighting stands to greatlyincrease the energy efficiency of many lighting applications includingstreet lighting, sign lighting, residential lighting, commerciallighting, etc.

SUMMARY OF THE INVENTION

Embodiments of the invention include LED lighting systems and methods.For example, in some embodiments, an LED lighting system is included.The LED lighting system can include a flexible layered circuit structurethat can include a top thermally conductive layer, a middle electricallyinsulating layer, a bottom thermally conductive layer, and a pluralityof light emitting diodes mounted on the top layer. The LED lightingsystem can further include a housing substrate and a mounting structure.The mounting structure can be configured to suspend the layered circuitstructure above the housing substrate with an air gap disposed inbetween the bottom thermally conductive layer of the flexible layeredcircuit structure and the housing substrate. The distance between thelayered circuit structure and the support layer can be at least about0.5 mm. In some embodiments, the flexible layered circuit structure isattached to the mounting structure in a releasable manner. In someembodiments, the flexible layered circuit structure is releasable fromthe mounting structure without the use of tools. In some embodiments,the flexible layered circuit structure is configured for replacement.

In some embodiments, an LED lighting system is included. The LEDlighting system can include a flexible layered circuit structure caninclude a top thermally conductive layer, a middle electricallyinsulating layer, a bottom thermally conductive layer, a plurality oflight emitting diodes mounted on the bottom layer, a housing substrate,and a mounting structure. The mounting structure can be configured tosuspend the layered circuit structure above the housing substrate withan air gap disposed in between bottom thermally conductive layer of theflexible layered circuit structure and the housing substrate, whereinthe distance between the layered circuit structure and the support layeris at least about 0.5 mm.

In some embodiments, a method for making an LED lighting system isincluded. The method for making an LED lighting system can includeobtaining a flexible layered circuit structure that can include, a topthermally conductive layer, a middle electrically insulating layer, abottom thermally conductive layer. The method can further includesuspending the flexible layered circuit structure above a housingsubstrate with an air gap disposed in between the bottom thermallyconductive layer of the flexible layered circuit structure and thehousing substrate, wherein the distance between the layered circuitstructure and the housing substrate is at least about 0.5 mm, andconnecting the flexible layered circuit structure to a power source.

In some embodiments, a method for operating an LED lighting system isincluded. The method for operating an LED lighting system can includeproviding electrical current to an LED lighting circuit, the LEDlighting circuit including a plurality of light emitting diodes, the LEDlighting circuit disposed upon a flexible layered circuit structure caninclude a top thermally conductive layer, a middle electricallyinsulating layer, a bottom thermally conductive layer, and dissipatingheat from the light emitting diodes to ambient air through the topsurface of the top thermally conductive layer and the bottom surface ofthe bottom thermally conductive layer.

In some embodiments, an LED lighting system is included. The LEDlighting system can include a flexible layered circuit structure caninclude a top thermally conductive layer, a middle electricallyinsulating layer, a bottom thermally conductive layer, a plurality oflight emitting diodes mounted on the top layer, the flexible layeredcircuit structure formed into a loop. The loop can be disposed within ahousing. The loop can be separated from the housing by an air gap. Theloop can be disposed sideways to the support structure.

This summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details are found inthe detailed description and appended claims. Other aspects will beapparent to persons skilled in the art upon reading and understandingthe following detailed description and viewing the drawings that form apart thereof, each of which is not to be taken in a limiting sense. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE FIGURES

The invention may be more completely understood in connection with thefollowing drawings, in which:

FIG. 1A is a cross sectional schematic view of a flexible layeredcircuit structure in accordance with various embodiments herein.

FIG. 1B is a cross sectional schematic view of a flexible layeredcircuit structure in accordance with various embodiments herein.

FIG. 1C is a cross sectional schematic view of a flexible layeredcircuit structure in accordance with various embodiments herein.

FIG. 1D is a cross sectional schematic view of a flexible layeredcircuit structure in accordance with various embodiments herein.

FIG. 2 is a schematic side view of a flexible layered circuit structurein accordance with various embodiments herein.

FIG. 3 is a schematic top view of a flexible layered circuit structurein accordance with various embodiments herein.

FIG. 4 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 5 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 6 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 7 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 8 is a schematic cut away top view of an LED lighting system inaccordance with various embodiments herein.

FIG. 9 is a schematic view of a portion of a mounting structure inaccordance with various embodiments herein.

FIG. 10 is a schematic view of a portion of a mounting structureinterfaced with a flexible layered circuit structure in accordance withvarious embodiments herein.

FIG. 11 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 12 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 13 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 14 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 15 is a schematic cross-sectional view of a flexible layeredcircuit structure in accordance with various embodiments herein.

FIG. 16 is a schematic cross-sectional view of a flexible layeredcircuit structure in accordance with various embodiments herein.

FIG. 17 is a schematic side view of an LED lighting system in accordancewith various embodiments herein.

FIG. 18 is a flowchart of a method of making an LED lighting system inaccordance with various embodiments herein.

FIG. 19 shows a top and cut away view exposing layers of a circuit boardwith connection pads in an embodiment of the present invention;

FIG. 20A shows a top view of top board pads and holes in an embodimentof the present invention;

FIG. 20B shows a bottom view of top board pads and holes in anembodiment of the present invention;

FIG. 21 shows a top view of bottom board receiving pad geometry in anembodiment of the present invention;

FIG. 22A shows a top view of an assembled board prior to joining in anembodiment of the present invention;

FIG. 22B shows a top view of joined boards in an embodiment of thepresent invention;

FIG. 23 shows a top profile view of an overlapping joint between boardsin an embodiment of the present invention;

FIG. 24 shows a top profile view of potting material used to strengthenand protect connection joints in an embodiment of the present invention;

FIG. 25 shows a side view of a joint assembly of a flexible strip withcurvature in an embodiment of the present invention;

FIG. 26A shows a top view of the top board for a mid-length connectionin an embodiment of the present invention;

FIG. 26B shows a bottom view of the top board for a mid-lengthconnection in an embodiment of the present invention;

FIG. 26C shows a top view of the bottom board for a mid-lengthconnection in an embodiment of the present invention;

FIG. 27 shows a top view of an overlapping connection used in striparray construction in an embodiment of the present invention;

FIG. 28 shows a top view of the construction of a two board by two boardgrid array in an embodiment of the present invention;

FIG. 29 shows construction of a larger grid using a two board by twoboard grid array in an embodiment of the present invention;

FIG. 30 shows another type of grid array wrapped around a cylindricalheat sink as an embodiment of the present invention;

FIG. 31A shows a top view of a board with a cut mark line for board orarray separation in an embodiment of the present invention;

FIG. 31B shows a top view of a board with a double line cut mark forboard or array separation in an embodiment of the present invention;

FIG. 31C shows the separation of two arrays of boards at one of the cutmarks in an embodiment of the present invention.

FIG. 32 is a schematic top view of two circuit boards connected withconnector in accordance with various embodiments herein;

FIG. 33 is a schematic top view of a top profile view of a connectorboard in accordance with various embodiments herein;

FIG. 34 is a schematic top profile view of an outline of routed panelready for component assembly and cutting in accordance with variousembodiments herein;

FIG. 35 is a schematic top profile view of a panel outline with endssheared off to expose boards in accordance with various embodimentsherein;

FIG. 36 is a schematic top profile view of panels joined by connectorsin accordance with various embodiments herein;

FIG. 37 is a schematic top profile view of circuit strips afterseparation in accordance with various embodiments herein;

FIG. 38 is a schematic top profile view of soldering of connector jointin accordance with various embodiments herein;

FIG. 39 is a schematic side profile view of an overlapping joint betweenboards in accordance with an alternate embodiment herein;

FIG. 40 is a schematic top profile view of panels joined by overlappingjoints in accordance with various embodiments herein;

FIG. 41 is a schematic top profile view of potting material used tostrengthen and protect connection joints in accordance with variousembodiments herein;

FIG. 42A is a schematic top view of top board pads and holes inaccordance with various embodiments herein;

FIG. 42B is a schematic bottom view of top board pads and holes inaccordance with various embodiments herein;

FIG. 43 is a schematic top view of bottom board receiving pad geometryin accordance with various embodiments herein;

FIG. 44A is a schematic top view of an assembled board prior to joiningin accordance with various embodiments herein;

FIG. 44B is a schematic top view of joined boards in accordance withvarious embodiments herein;

FIG. 45 is a schematic side view of a joint assembly of a flexible stripwith curvature in accordance with various embodiments herein;

FIG. 46 is a process flow diagram for construction of multi-boardassemblies in strip or matrix form in accordance with variousembodiments herein.

FIG. 47 is a schematic top view of a plurality of circuit boards withholding apparatus in accordance with various embodiments herein.

FIG. 48 is a schematic view of two circuit boards with solder pad andplated hole features in the top circuit board and with mating solder padfeatures on the bottom circuit board in accordance with variousembodiments herein.

FIG. 49 is a schematic view of two circuit boards with prepared solderpads prior to attachment in accordance with various embodiments herein.

FIG. 50 is a schematic view of a successful solder joint resulting fromreflow soldering of a prepared lap joint held by an apparatus and reflowor wave soldered in accordance with various embodiments herein.

FIG. 51 is a schematic view of a circuit board clamp in accordance withvarious embodiments herein.

FIG. 52 is a schematic view of a circuit board clamp in accordance withvarious embodiments herein.

FIG. 53 is a schematic view of a plurality of top and bottom circuitboards each as part of an array of circuit boards arranged parallel toone another with electronic components prepared for soldering inaccordance with various embodiments herein.

FIG. 54 is a schematic illustration showing the solder connecting aplurality of long continuous circuit boards forming circuit board stripsin accordance with various embodiments herein.

FIG. 55 is a schematic top view of a plurality of circuit board clampsholding top and bottom circuit boards together in accordance withvarious embodiments herein.

FIG. 56 is a schematic bottom view of a plurality of circuit boardclamps holding top and bottom circuit boards together in accordance withvarious embodiments herein.

FIG. 57 is a schematic view of a circuit board with circuit board clampsallowing for a visual inspection step in accordance with variousembodiments herein.

FIG. 58 is a schematic view of a reflow solder oven with conveyor beltfeeds in and out of the machine in accordance with various embodimentsherein.

FIG. 59 is a schematic view of a wave solder machine with feeds in andout of tank in accordance with various embodiments herein.

FIG. 60 is a flow diagram of a method with unpopulated, pre-populated,and pre-populated/soldered plurality of circuit boards in accordancewith various embodiments herein.

FIG. 61 is a schematic top view of top circuit boards and bottom circuitboards ready for attachment that are pre-populated and pre-soldered withelectronic components.

FIG. 62 is a schematic top view of top circuit boards and bottom circuitboards ready for attachment with electrical component positions that areleft unpopulated.

FIG. 63 is a schematic view of a continuous plurality of solderedpanelized circuit boards in accordance with various embodiments herein.

While the invention is susceptible to various modifications andalternative forms, specifics thereof have been shown by way of exampleand drawings, and will be described in detail. It should be understood,however, that the invention is not limited to the particular embodimentsdescribed. On the contrary, the intention is to cover modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention described herein are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art canappreciate and understand the principles and practices of the presentinvention.

All publications and patents mentioned herein are hereby incorporated byreference. The publications and patents disclosed herein are providedsolely for their disclosure. Nothing herein is to be construed as anadmission that the inventors are not entitled to antedate anypublication and/or patent, including any publication and/or patent citedherein.

Solid state lighting stands to greatly increase the energy efficiency ofmany lighting applications including street lighting, sign lighting,residential lighting, commercial lighting, etc. However, one designchallenge associated with LED lighting systems is the dissipation ofheat. In particular, it is important consider the junction temperaturein an LED (the p-n junction temperature) lighting system. If thistemperature rises above the prescribed level recommended by the LEDmanufacturer, the lifetime of the LED as well as its intensity and colormay be affected.

Mounting an LED carrying circuit on a heat sink, or adding secondaryheat sinks is one approach to heat dissipation. However, this can addadditional cost to the finished product in addition to constrainingdesign flexibility. Applicants have developed various embodiments of LEDlighting systems that can provide sufficient heat dissipation withoutthe need for directly mounting the LED carrying circuit onto a largeheat sink or any substantial secondary heat sinks. Such embodiments cansuccessfully maintain the junction temperature of the LEDs below thecritical temperature.

Referring now to FIG. 1A, a cross sectional schematic view is shown of aflexible layered circuit structure 100 in accordance with variousembodiments herein. The flexible layered circuit structure can include atop thermally conductive layer 102, a middle electrically insulatinglayer 104, and a bottom thermally conductive layer 106. In someembodiments, the top, middle, and bottom layers combined have a thermalresistance of less than 10 degrees Celsius per Watt. A plurality oflight emitting diodes 108 can be mounted on the top thermally conductivelayer 102. When electrical current is passed through the circuit on thetop surface of the top thermally conductive layer, one or more of theLEDs can be energized and emit visible light.

In some embodiments, a commercially available FR4 material can be usedas a starting material and is modified to create the layered circuitstructure. The FR4 material preferably includes a layer of fiberglasssandwiched between two layers of copper. An example of a suitable FR4material is FR406 manufactured by Isola Group of Chandler, Ariz. The toplayer can include one of the two layers of copper, the intermediatelayer can include a layer of fiberglass, and the bottom layer caninclude the other of the two layers of copper. It is recognized thatother suitable FR4 materials could be used and that these layers couldbe either manufactured or purchased in this form.

Prior to modification, the top layer can be copper approximately 0.5 to4.0 ounces per square foot and approximately 0.0007 to 0.0056 inchthick, 0.25 to 48.00 inches wide, and 0.50 to 48.00 inches long.Although copper is a preferred material, it is recognized that othersuitable electrically conductive materials such as but not limited toaluminum could be used. The top, copper layer can be modified to includea thermally conductive printed or etched electrical circuit usingstandard electrical circuit design tools and techniques well known inthe art and can then be coated with a protective coating using standardsolder masking and labeling techniques. An example of a suitableprotective coating that could be used is TechniMask ISR 1000manufactured by Technic, Inc. of Cranston, R.I. The top layer can bedesigned in such a way as to provide receptacles and mounting surfacesfor LEDs and other SMT electrical components proximate the top surface.

The intermediate layer can be an electrically insulating thermallyconductive layer, in some embodiments made of fiberglass approximately0.005 to 0.020 inch thick, 0.25 to 48.00 inches wide, and 0.50 to 48.00inches long. The fiberglass has a breakdown voltage of greater than 5kilovolts (kV), a tensile strength of 55 kips per square inch (ksi), anda flexural strength of 91 kips per square inch (ksi). The thermalconductivity of the fiberglass can be 0.3 to 0.4 Watts per meter perdegrees Kelvin (W/mK). Although fiberglass is a preferred material, itis recognized that other suitable materials such as but not limited topolymer or ceramic blended dielectrics may be used.

Prior to modification, the bottom layer can be copper approximately 0.5to 4.0 ounces per square foot and can be approximately 0.0007 to 0.0056inch thick, 0.25 to 48.00 inches wide, and 0.50 to 48.00 inches long.Although copper is a preferred material, it is recognized that othersuitable electrically conductive materials such as but not limited toaluminum could be used. The bottom, copper layer can be modified into aheat spreading copper circuit laterally and along its longitudinal axisproximate the bottom surface in order to rapidly spread the heat throughthe bottom layer. In some embodiments, the exposed copper proximate thebottom surface of the bottom layer can then be tinned. The bottom layercan include thermally conductive printed circuits, which are printed oretched using solder mask printing, photo etching, and solder maskingtechniques well known in the art for producing electrical circuits. Invarious embodiments, the bottom layer can include solid coverage ofthermally conductive material (such as copper) across an area equal to amajority of the surface area with no direct electrical connection to thetop layer.

The flexible layered circuit structure can be at least semi-flexible insome embodiments, not rigid. The flexible layered circuit structure canbe any desired length, which could be as long as 250 feet or more. Thestrip can bend (for example along the lengthwise axis in a directionfrom the top of the flexible layered circuit structure to the bottom ofthe flexible layered circuit structure, or bottom to top) sufficientlyto achieve a radius of curvature of 6 inches. In some embodiments, thestrip can bend sufficiently to achieve a radius of curvature of 1 inch.In some embodiments, the flexible layered circuit structure can bewrapped about the hub of a reel for storage until use. The flexiblelayered circuit structure can also twist relative to its longitudinalaxis up to 10 degrees per inch.

In some embodiments, light emitting diodes can be mounted on the bottomlayer of the flexible layered circuit structure. Referring now to FIG.1B, a cross sectional schematic view is shown of a flexible layeredcircuit structure 110 in accordance with various embodiments herein. Theflexible layered circuit structure 110 can include a top thermallyconductive layer 102, a middle electrically insulating layer 104, and abottom thermally conductive layer 106. A plurality of light emittingdiodes 108 can be mounted on the bottom thermally conductive layer 106.

In some embodiments, light emitting diodes can be mounted on both thetop and the bottom layers of the flexible layered circuit structure.Referring now to FIG. 1C, a cross sectional schematic view is shown of aflexible layered circuit structure 120 in accordance with variousembodiments herein. The flexible layered circuit structure 120 caninclude a top thermally conductive layer 102, a middle electricallyinsulating layer 104, and a bottom thermally conductive layer 106. Aplurality of light emitting diodes 108 can be mounted on the topthermally conductive layer 102 and the bottom thermally conductive layer106.

When light emitting diodes are mounted on both the top thermallyconductive layer 102 and the bottom thermally conductive layer 106, itwill be appreciated that the light emitting diodes can be placeddirected opposite on another (such as in FIG. 1C) or they can be offsetfrom one another to avoid the concentration of too much heat in aparticular spot. Referring now to FIG. 1D, a cross sectional schematicview is shown of a flexible layered circuit structure 130 in accordancewith various embodiments herein. The flexible layered circuit structure130 can include a top thermally conductive layer 102, a middleelectrically insulating layer 104, and a bottom thermally conductivelayer 106. A plurality of light emitting diodes 108 can be mounted onthe top thermally conductive layer 102 and the bottom thermallyconductive layer 106, but offset such that the positions of the lightemitting diodes 108 on the top do not match with the positions of thelight emitting diodes 108 on the bottom.

It will be appreciated that flexible layered circuit structures as usedin various embodiments herein can be either be unitary segments or canbe formed of multiple segments that are bonded to on another at joints.Referring now to FIG. 2, a schematic side view is shown of a flexiblelayered circuit structure 200 in accordance with various embodimentsherein. In this view, it can be seen that the flexible layered circuitstructure is formed of a first segment 202, a second segment 204, and athird segment 206. The first segment 202 is bonded to the second segment204 at a first overlapping joint 208. The first overlapping joint 208can provide electrical communication between the circuitry on the firstsegment 202 and the circuitry on the second segment 204. The secondsegment 204 is bonded to the third segment 206 at a second overlappingjoint 210. The second overlapping joint 210 can provide electricalcommunication between the circuitry on the second segment 204 and thecircuitry on the third segment 206. Connections between segments cancontinue in this manner such that the overall length of the flexiblelayered circuit structure can be as long as it desired.

Referring now to FIG. 3, a schematic top view is shown of a portion 300of the flexible layered circuit structure 200 of FIG. 2. The flexiblelayered circuit structure includes a top thermally conductive layer 302.A plurality of light emitting diodes 308 are mounted on the topthermally conductive layer 302. A variety of circuitry and/or components330 can be etched into or mounted on the top thermally conductive layer302. The circuitry and components 330 can include various itemsincluding, but not limited to, resistors, capacitors, traces, lineardrivers, and the like. An example of a suitable LED is NS3W083Amanufactured by Nichia Corporation of Detroit, Mich. An example of asuitable liner driver is NUD4001 manufactured by ON Semiconductor ofPhoenix, Ariz.

In some embodiments, the light emitting diodes mounted on the top layerhave a power of between 0.25 and 3 watts per inch squared of the surfacearea of the bottom layer.

In various embodiments, a mounting structure can be used to suspend theflexible layered circuit structure above a housing substrate. It will beappreciated that the mounting structure can take on many differentforms. Referring now to FIG. 4, a schematic side view is shown of an LEDlighting system 400 in accordance with various embodiments herein. TheLED lighting system 400 can include a flexible layered circuit structure402 and electrical leads 414 to provide electrical current to theflexible layered circuit structure 402. The flexible layered circuitstructure 402 can be suspended above a housing substrate 408, such thatthere is an air gap 410 disposed in between the bottom thermallyconductive layer of the flexible layered circuit structure 402 and thehousing substrate 408. In some embodiments, the air gap 410 is presentunder at least about 80% of the surface area of the bottom of theflexible layered circuit structure 402. A mounting structure can be usedto suspend the flexible layered circuit structure. In this embodiment,the mounting structure can include one or more posts 406 or standoffs.The posts 406 can serve to hold the flexible layered circuit structure402 in place. In some embodiments, the posts can be configured to exerttension on the flexible layered circuit structure in the direction ofthe lengthwise axis of the flexible layered circuit structure such thatit is maintained taut.

The air gap 410 can be of various sizes. In some embodiments, the airgap can be at least about 0.5 mm. In some embodiments, the air gap canbe from between 0.5 mm and 100 mm. In some embodiments, the air gap canbe from between 1 mm and 50 mm. In some embodiments, the air gap can befrom between 2 mm and 25 mm. In some embodiments, the air gap can bebetween about 40% and 60% of the width of the flexible layered circuitstructure.

The air gap can serve to promote heat dissipation off of the bottomlayer of the flexible layered circuit structure. In particular, the LEDlighting system can be configured so as to have thermal transferproperties sufficient to allow the system to maintain a thermalequilibrium at or below the critical junction temperatures for the LEDswithout the need for the addition of secondary heat sinking. Thecritical junction temperatures can vary based on the specific LED modeland manufacturer. However, critical junction temperatures can range from100 degrees Celsius or less for some LED models to 150 degrees Celsiusor more for others. In some embodiments, the junction temperature can bekept below 150 degrees Celsius. In some embodiments, the junctiontemperature can be kept below 140 degrees Celsius. In some embodiments,the junction temperature can be kept below 130 degrees Celsius. In someembodiments, the junction temperature can be kept below 120 degreesCelsius. In some embodiments, the junction temperature can be kept below110 degrees Celsius. In some embodiments, the junction temperature canbe kept below 100 degrees Celsius. In some embodiments, the junctiontemperature can be kept below 90 degrees Celsius.

In various embodiments, the mounting structure can include manydifferent specific structural elements. By way of example, in someembodiments, the mounting structure can include a fastener, a hook, apin, a clip, a spring clip, a tab and/or tab receptacle. In variousembodiments, the mounting structure can be directly or indirectlyattached to the housing substrate. In some embodiments, the flexiblelayered circuit structure can be attached to the mounting structure in areleasable manner. In some embodiments, the flexible layered circuitstructure can be releasable form the mounting structure in such a waythat specialized tools are not required and thus the flexible layeredcircuit structure can be released from the mounting structure by hand.In this manner, the flexible layered circuit structure can be configuredfor replacement. In some embodiments, the mounting structure can be usedto align the flexible layered circuit structure with secondary optics ora diffuser.

The housing substrate can include many different materials. In someembodiments, the housing substrate can include organic or inorganicstructural materials. In some embodiments, the housing substrate can bea material including, but not limited to, metals, polymers, cellulosicmaterials, composites, glass, stone and the like. In variousembodiments, the housing substrate can be opaque, transparent, orsemi-transparent.

It will be appreciated that the mounting structure can be attached tothe flexible layered circuit structure in many different ways. Forexample, in the context of posts, the posts can attach to the bottom,side, or ends of the flexible layered circuit structure. In someembodiments, the flexible layered circuit structure can includestructural features so as to facilitate connection with the mountingstructure. By way of example, in some embodiments the flexible layeredcircuit structure can define notches or apertures in order to facilitateconnection with the mounting structure. Referring now to FIG. 5, aschematic top view is shown of a portion of an LED lighting system inaccordance with various embodiments herein. The flexible layered circuitstructure includes a top thermally conductive layer 502. A plurality oflight emitting diodes 508 are mounted on the top thermally conductivelayer 502. A variety of circuitry 530 can be etched into or disposed onthe top thermally conductive layer 502. In addition, a plurality ofapertures 532 are formed in the flexible layered circuit structure.These apertures 532 can be configured to engage a mounting structure, ora portion thereof.

Referring now to FIG. 6, a schematic side view is shown of an LEDlighting system 600 in accordance with various embodiments herein. Inthis embodiment, the flexible layered circuit structure 602 carrying thelight emitting diodes 608 is oriented on its side (or lateral side orlateral edge) relative to posts 606, which can serve as a mountingstructure to maintain an air gap in between the flexible layered circuitstructure 602 and the housing substrate 610. As such, in this embodimentthe mounting structure can engage a lateral side of the flexible layeredcircuit structure.

Referring now to FIG. 7, a schematic side view is shown of an LEDlighting system 700 in accordance with various embodiments herein. Inthis view, the flexible layered circuit structure 702 is suspended abovethe housing substrate 708 through mounting structure elements 706. Inthis case, the ends of the flexible layered circuit structure interfacewith the mounting structure elements 706, however, it will beappreciated that other portions of the flexible layered circuitstructure 702 can interface with the mounting structure elements 706.

Referring now to FIG. 8, a schematic cut away top view is shown of anLED lighting system 700 in accordance with various embodiments herein.In this view, one example of how the flexible layered circuit structure702 can be attached to the mounting structure elements 706 is shown. Theflexible layered circuit structure 702 can define notches 703 near theends of the flexible layered circuit structure 702. The mountingstructure elements 706 can include an engagement member 710 that passesinto the notches 703 in order to grip the flexible layered circuitstructure 702. The mounting structure elements 706 can also include atensioner 712. The tensioner 712 can provide spring force in order toapply tension to the flexible layered circuit structure in order to makeit taut. In some embodiments, the tensioner 712 can be configured tomaintain a tension force of at least about one ounce (0.28 N). Thetensioner 712 can be configured to maintain a tension force on theflexible layered circuit structure despite thermal expansion of theflexible layered circuit structure. By way of example, in someembodiments, the tensioner can be configured to maintain a tension forceof at least one ounce (0.28 N) despite thermal expansion of the flexiblelayered circuit structure of up to 1 millimeter per meter in length ofthe flexible layered circuit structure. In some embodiments, thetensioner 712 can include a spring. In some embodiments, the mountingstructure is used to take up variable length or mechanical tolerances inthe construction of the flexible layered circuit structure.

Referring now to FIG. 9, a schematic view of a portion of a mountingstructure 800 is shown in accordance with various embodiments herein.The mounting structure 800 can include tabs 824 (or projections). Themounting structure 800 can include a body portion 822 and an aperture828 to facilitate mounting to another component such as a housingsubstrate. Referring now to FIG. 10, a schematic view of a portion of amounting structure 800 interfaced with a flexible layered circuitstructure 802 is shown in accordance with various embodiments herein. Inthis view, it can be seen that the tabs 824 fit within the notches 830in the flexible layered circuit structure to support it and hold it inplace. In addition, the body portion 822 can be capable of being flexedto generate a spring force that can be exerted on the flexible layeredcircuit structure 802. In this embodiment, the mounting structure for asingle end of the flexible layered circuit structure can be formed of asingle piece of material, such as a metal or a polymer. However, inother embodiments the mounting structure can include multiple pieces ofmaterial.

Referring now to FIG. 11, a schematic side view is shown of an LEDlighting system 900 in accordance with various embodiments herein. TheLED lighting system 900 can include a flexible layered circuit structure902. The flexible layered circuit structure 902 can be suspended above ahousing substrate 910, such that there is an air gap 914 disposed inbetween the bottom thermally conductive layer of the flexible layeredcircuit structure 902 and the housing substrate 910. A mountingstructure can be used to suspend the flexible layered circuit structure.In this embodiment, the mounting structure can include one or moreblocks 906. The blocks 906 can serve to hold the flexible layeredcircuit structure 902 in place. In some embodiments, the posts can beconfigured to exert tension on the flexible layered circuit structure inthe direction of the lengthwise axis of the flexible layered circuitstructure such that it is maintained taut (e.g., the tension is exertedin a direction away from the middle of the flexible layered circuitstructure). In some embodiments, a tensioner 912 can be disposed betweenthe block 906 and the flexible layered circuit structure 902. In thisembodiment, for example, the tensioner 912 can include a spring-loadedconnection point (such as a hook or tab receptacle) to exert tension onthe flexible layered circuit structure 902. In some embodiments, thetensioner 912 can be configured to move with respect to the block 906 inorder to apply tension to the flexible layered circuit structure 902. Byway of example, the block 906 can move within a channel formed in theblock 906.

Referring now to FIG. 12, a schematic side view is shown of an LEDlighting system 1000 in accordance with various embodiments herein. TheLED lighting system 1000 can include a flexible layered circuitstructure 1002. Light emitting diodes 1008 can be mounted on theflexible layered circuit structure 1002. The flexible layered circuitstructure 1002 can be suspended inside a cavity defined by a housingsubstrate 1010. There can be an air gap 1016 disposed in between theflexible layered circuit structure 1002 and the housing substrate 1010.Leads 1014 can be arranged to provide electrical current to the flexiblelayered circuit structure 1002.

Referring now to FIG. 13, a schematic side view is shown of an LEDlighting system 1100 in accordance with various embodiments herein. TheLED lighting system 1100 can include a flexible layered circuitstructure 1102. Light emitting diodes 1108 can be mounted on theflexible layered circuit structure 1102. In this embodiment, theflexible layered circuit structure 1102 can assume a U shape such thatthe first end 1118 and the second end 1120 are disposed adjacent to oneanother. The flexible layered circuit structure 1102 can be suspendedinside a cavity defined by a housing substrate 1110. There can be an airgap 1116 disposed in between the flexible layered circuit structure 1102and the housing substrate 1110. Leads 1114 can be arranged to provideelectrical current to the flexible layered circuit structure 1102.

Referring now to FIG. 14, a schematic side view is shown of an LEDlighting system 1200 in accordance with various embodiments herein. TheLED lighting system 1200 can include a flexible layered circuitstructure 1202 and electrical leads to provide electrical current to theflexible layered circuit structure 1202. Material can be disposed overthe top of flexible layered circuit structure 1202 (and thus over thetop of LEDs in various embodiments) such as optics 1210, secondaryoptics, or a diffuser. The flexible layered circuit structure 1202 canbe suspended above a housing substrate 1208, such that there is an airgap disposed in between the bottom thermally conductive layer of theflexible layered circuit structure 1202 and the housing substrate 1208.A mounting structure can be used to suspend the flexible layered circuitstructure. In this embodiment, the mounting structure can include one ormore posts 1206 or standoffs.

It will be appreciated that various modifications can be made in orderto enhance heat dissipation in the system. By way of example, variousmodifications can be made to the flexible layered circuit structure inorder to enhance heat dissipation. Referring now to FIG. 15, a schematiccross sectional view is shown of a flexible layered circuit structure1300 in accordance with various embodiments herein. The flexible layeredcircuit structure can include a top thermally conductive layer 1302, amiddle electrically insulating layer 1304, and a bottom thermallyconductive layer 1306. A plurality of light emitting diodes 1308 can bemounted on the top thermally conductive layer 1302. A coating 1310 canbe disposed on the bottom thermally conductive layer 1306, the coating1310 comprising a material with properties that enhance heat transfer.For example, in some embodiments, the coating can be a thermallyconductive and emissive material. In some embodiments, the coating canbe a material such as tinning.

In some embodiments, additional structural features can be disposed onthe bottom layer in order to assist in heat dissipation. By way ofexample, structural features including, but not limited to, heat slugs,cooling fins, heat conductive projections, and the like can be mountedon the bottom surface of the bottom layer in order to aid in heatdissipation.

In some embodiments, the flexible layered circuit structure can bealtered in order to enhance heat transfer. Referring now to FIG. 16, aschematic cross sectional view is shown of a flexible layered circuitstructure 1400 in accordance with various embodiments herein inaccordance with various embodiments herein. The flexible layered circuitstructure can include a top thermally conductive layer 1402, a middleelectrically insulating layer 1404, and a bottom thermally conductivelayer 1406. A plurality of light emitting diodes 1408 can be mounted onthe top thermally conductive layer 1402. In this embodiment, the bottomsurface 1420 of the bottom thermally conductive layer 1406 can have asurface topology that is different than a standard flat surface. By wayof example, the surface can have numerous peaks and valleys (or betextured) in order to increase the surface area.

In some embodiments, the textured surface can have a surface area atleast 10 percent greater than an equally sized substantially flatsurface. In some embodiments, the textured surface can have a surfacearea at least 20 percent greater than an equally sized substantiallyflat surface. In some embodiments, the textured surface can have asurface area at least 30 percent greater than an equally sizedsubstantially flat surface. In some embodiments, the textured surfacecan have a surface area at least 40 percent greater than an equallysized substantially flat surface. In some embodiments, the texturedsurface can have a surface area at least 80 percent greater than anequally sized substantially flat surface. In some embodiments, thetextured surface can have a surface area at least 100 percent greaterthan an equally sized substantially flat surface.

Referring now to FIG. 17, a schematic side view is shown of an LEDlighting system 1500 in accordance with various embodiments herein. TheLED lighting system 1500 can include a flexible layered circuitstructure 1502 and electrical leads to provide electrical current to theflexible layered circuit structure 1502. The flexible layered circuitstructure 1502 can be suspended above a housing substrate 1508, suchthat there is an air gap 1510. The top surface 1524 of the housingsubstrate 1508 can be coated with a layer of material 1522 to enhanceheat flow across the air gap 1510.

In some embodiments, a fan can be included to enhance heat dissipationby causing movement of air over surfaces of the flexible layered circuitstructure.

It will be appreciated that various methods are also included herein.The method for making an LED lighting system can include obtaining aflexible layered circuit structure that can include, a top thermallyconductive layer, a middle electrically insulating layer, a bottomthermally conductive layer. The method can further include suspendingthe flexible layered circuit structure above a housing substrate with anair gap disposed in between the bottom thermally conductive layer of theflexible layered circuit structure and the housing substrate, whereinthe distance between the layered circuit structure and the housingsubstrate is at least about 0.5 mm, and connecting the flexible layeredcircuit structure to a power source.

In some embodiments, suspending includes attaching the flexible layeredcircuit structure to a mounting structure. In some embodiments, themounting structure provides the connection to the power source. In someembodiments, the method can further include cutting the flexible layeredcircuit structure to a desired length. In some embodiments, the methodcan include unwinding the flexible layered circuit structure from astorage reel prior to cutting. In some embodiments, suspending caninclude attaching the flexible layered circuit structure to a mountingstructure that provides a tension force along the length of the flexiblelayered circuit structure. In some embodiments, the method can furtherinclude applying a tension force of at least one ounce (0.28 N) to theflexible layered circuit structure. In some embodiments, the method canfurther include removing the flexible layered circuit structure from theposition suspended above a housing substrate. In some embodiments, theaction of removing the flexible layered circuit structure can beaccomplished without tools. In some embodiments, the method can furtherinclude replacing the flexible layered circuit structure with anotherflexible layered circuit structure.

Referring now to FIG. 18, a flow chart is shown of a method of making anLED lighting system in accordance with various embodiments herein. Themethod can include an operation of obtaining a flexible layered circuitstructure 1602. Optionally, in some embodiments, the method can furtherinclude an operation of cutting the flexible layered circuit structureto a desired length 1604. In various embodiments, the method can furtherinclude an operation of suspending the flexible layered circuitstructure above a housing substrate 1606. In some embodiments, themethod can further include an operation of connecting the flexiblelayered circuit structure to a power source 1608. Optionally, in someembodiments, the method can include a step of replacing the flexiblelayered circuit structure with another flexible layered circuitstructure 1610. In various embodiments the flexible layer circuitstructure can be removed, and optionally replaced, without the use oftools (for example without the need to remove soldering from elements ofthe system).

In some embodiments, a method for operating an LED lighting system isincluded. The method for operating an LED lighting system can includeproviding electrical current to an LED lighting circuit, the LEDlighting circuit including a plurality of light emitting diodes, the LEDlighting circuit disposed upon a flexible layered circuit structure caninclude a top thermally conductive layer, a middle electricallyinsulating layer, and a bottom thermally conductive layer. The methodcan further include dissipating heat from the light emitting diodes toambient air through the top surface of the top thermally conductivelayer and the bottom surface of the bottom thermally conductive layer.

Embodiments of the present invention described below describeinterconnections providing advantages over both traditional and morerecent methods of interconnect such as the newly introduced FlexRAD™system of continuous connection. Embodiments of the present inventioninclude aspects addressing the strength, reliability and usability ofinterconnects between the semi-flexible substrates in order to producelong strips or continuous reels for ease in fixture assembly.

Embodiments of the present invention provide for a thin board substrate,which makes the connector flexible enough to conform to normalvariations of board thickness, solder height and mechanical mountingheight differences. The thin board substrate allows heat and solder toeasily flow through the connector from top to bottom. An electricalinsulating layer within the thin board is both thin enough to enable ahigh degree of thermal conductivity and is able to maintain high levelsof breakdown isolation. The material chosen for the electricallyinsulating layer enhances thermal conductivity.

The thin board substrate adds flexibility to the connection, reducingstress at the solder joint associated with the use of rigid pins andother types of connectors. This assists in preventing tearing of theprinted circuit board pads on the board when bending stresses areintroduced. The thin board substrate materials and thicknesses assist inhandling solder melt temperatures without delamination or damage. Copperpads on the bottom side of the connector are designed to match the padsof the boards to be connected; in spacing, area and thermalcharacteristics.

Copper pads on a top side can receive heat (e.g., from a soldering iron)and provide a path for conduction through the electrically insulatingsubstrate and/or a plated through hole to the pads on the bottom. Thecopper conductors are used to connect the pads to be mated to theprinted circuit boards. The copper conductors can be thick toaccommodate high currents. Copper conductors can be run on top or underthe connector insulating substrate, depending on requirements forisolation, current carrying capacity and protection.

Embodiments of the present invention provide for copper foils designedto maintain gap distances between connections for electrical isolation.Connections and conductors are protected from damage or shorting bybeing covered by the connector body. Connections and conductors can befurther protected from moisture by the simple addition of an under filllayer of potting material, an encapsulent or an overcoat of pottingmaterial or encapsulant.

Plated holes located at the pad positions, through the connector boardallow solder and heat to flow down into the connection both tofacilitate solder connections and to enable rapid connection. The platedholes located at the pad positions take up excess solder when solderpaste is used to make connections or when solder is applied manually.The plated holes located at the pad positions can be used to storesolder paste for later reflow.

Embodiments of the present invention provide for sealing of solder pastein the holes at the pad positions so the paste remains fresh for lateruse. The sealing may include a thin solder layer, a thin flux layer or athin plastic or metallic peel-off material.

Angled or other geometric patterns in the pad and copper conductorssupport connections for offset or angled printed circuit boards.Multiple pad sets and associated conductor connections allow splittingof conduction paths.

A masking coating over the top and the bottom of the connector board(open at the pads), reduces the opportunity for solder shorts andimprove the appearance of the connector. The masking material can bechosen to match the color and characteristics of the boards beingjointed to minimize the visibility of the connector.

The connectors can be easily formed for vertical step offsets.Connectors onto which other circuits can be used, including pads andgeometries for wire or other conventional types of connectors, as wellas terminations and active circuitry. The connectors can be stackable.Connectors with substrate can extend well beyond pad areas providingmechanical support. Connectors with additional pads can provideadditional strain relief.

The pad geometries may match existing pinned connectors to allow anoption to alternate use of pinned connectors. The thin board can bedesigned to be cut with scissors or a simple shear. Printed lines at thetop of the strip or matrix can show expected cut lines; providingguidance. Copper pads, holes and conductors can be a sufficient spacefrom the cutting location to assure only electrically insulatingsubstrate will be cut.

Embodiments of the present invention provide for intimate contactbetween metal pads with minimal fill layer of solder to increase jointstrength. Larger pads can be used to increase the strength, both becauseof the larger solder contact area, but also because of the larger areasof contact and adhesion between pad and insulating substrate. Largerareas of conductor surrounding exposed, soldered pad apertures increasethe strength both by offering more area for adhesion between conductorsand the insulating substrate, but also because they add to the conductorstructure. The spacing of the pads for maximum array width and heightincreases the joint strength against shear and rotational forces andtorques. A space between pad and edges of the board can be maintained toincrease strength by decreasing leverage and converting stresses intosurface pressures away from the joint.

Embodiments of the present invention disclose increasing the number ofholes leading from the top surface to the pad, which increases thestrength by adding more areas of solder fill. The increased number ofholes also increases the probability of having a better percentage ofsolder fill. The choice of solder type and composition can have animpact on joint strength. Lead baring solders have lower tensilestrength then their lead free counterparts. Higher tensile strengthincreases the fracture strength of the connection.

Embodiments of the present invention provide for the application ofthermal tape or adhesive across the bottom side of the joint to increasejoint strength. The application of potting material or other adhesivesor coatings of the structure adds additional strength to the joint. Inthe areas of board overlap, excluding the conductive pad locations,adhesive can be added to increase joint strength.

Embodiments of the present invention enable connection of two or morecircuit boards to construct various forms, including linear strips andtwo and three dimensional arrays and matrix forms. Embodiments of thepresent invention include construction of flat grids of circuit boards,as well as grids able to be formed around curved surfaces or sharpcorners. In alternate embodiments three dimensional shapes may beformed.

With reference to FIG. 19, a top and cut away view exposing layers of acircuit board with connection pads in an embodiment of the presentinvention is shown. The circuit board 1909 can have two electricallyconductive layers 1930, 1932 with a thin electrical isolating material1931 sandwiched in between. The inventors chose the electricallyconductive layers to be 2 oz. copper. The inventors also chose the innerinsulating layer to be 0.012 inch thick fiberglass composite material.Circuit paths of various designs can be etched into the top and bottomconductive layers 1930, 1932 to produce the circuit conductive paths.Plated through holes 1902 can be added at metal pads 1903 and platedthrough with conductive metal to form a connection between top andbottom. Additional thin layers of non-conductive solder repellingmaterial 1905 (solder masks) can be added to the top and bottom of theboard 1909 to restrict the movement of solder and protect the circuitpaths from the pads 1903. The solder mask 1905 is interrupted to exposeconductive pads 1904 for mounting electronic components 1913, as well aspads 1903 used for board interconnect. On top of the solder mask 1910,visible markings may be printed consisting of text and other circuitmarkings, and special alignment marks 1911, 1917 (FIG. 20A), 28 (FIG.26C) and 29 (FIG. 26A) or cut marks 1933, 1934 (FIG. 31C).

In one embodiment the circuit boards 1901 (FIG. 20A) and 1909 consistedof a thin, low thermal mass substrate base material comprised of twoelectrically conductive layers with a thin, electrically isolatingmaterial sandwiched in between. Electrically conductive layers used forproof of concept testing consisted of 2 oz. copper. The thin,semi-flexible circuit boards can be designed with regions of conductorsand pads allowing them to function as connectors, enabling the mating ofone board to another. The circuit board consists of a thin, low thermalmass substrate base material comprised of two electrically conductivelayers with a thin, electrically isolating material sandwiched inbetween. Electrically conductive layers used were of 2 oz. copper. Theinner insulating layer was chosen to be 0.012 inch thick fiberglasscomposite material. Both of these are common to circuit boardfabrication, however generally used for inner layers of a multilayercircuit board, not for circuit board in completion. Circuit patterns1960 (FIG. 22B) of various designs were etched into the top and bottomconductive layers to produce the circuit conductive paths. Holes 1902are added at the pad locations 1903 and plated through with conductivemetal to form a connection between top and bottom. Additional thinlayers of non-conductive, solder repelling material 1905 (solder masks)were added to the top and bottom of the board to restrict the movementof solder and protect the circuit paths away from the pads.

Circuit materials and thicknesses are of a design which allows circuitboards 1901, 1909 to be cut with a conventional shear or scissors 1937at any of several locations enabling later trimming to length orseparation. It is fully contemplated circuit boards could be laser cutas well to obtain individual circuit strips or arrays. Electricalcomponents, including LED emitters can be assembled onto circuit boardsby conventional methods of electronic solder assembly.

Copper conductors can be used for connecting pads 1904, 1903 to be matedwith other electronic components 1913. These are etched or formed fromthe conductive layers 1930, 1932 described above. These circuit pathscan be printed in almost any pattern commonly used in circuit boards andcan be patterned to receive electronic components 1913 such as LEDs 1914or integrated circuits. The copper conductors can be very thick and wideto accommodate high currents. In an embodiment 2 oz. copper was usedwith a conductor width of 0.040 inch to enable a low voltage drop acrossthe connector when carrying up to 5 amps of current.

It is recognized there may be one or more conductive layers in thecircuit board structure.

Copper foils are designed to maintain gap distances between connectionsfor electrical isolation. In an embodiment, voltage isolations of up to500 V were maintained by maintaining a distance of 0.025 inches betweencopper foils. By increasing the spacing, substantially higher isolationscan be achieved. Copper conductors can be run on top of or under theconnector insulating substrate, depending on requirements for isolation,current carrying capacity and protection.

Circuit boards 1901, 1909 can incorporate a variety of circuits,including pads and geometries for wire or other conventional types ofconnectors, as well as being able to incorporate terminations and activecircuitry. The thin circuit board described above is particularly wellsuited because of its high thermally conductive structure for power andheat creating circuits. In one implementation, the circuitry for highcurrent driver 19013 (e.g., one semiconductor #NUD4001 operating at 24VDC) along with a LED string 1914 was added to the top side of theboard. Both the top side FIG. 20A and bottom side FIG. 20B of the boardwere designed with large metal (e.g., copper) foils and pads which couldtranslate heat through the thin insulating material 1931 by effectivelycreating a large area for heat transfer from the top copper layer 1930through the less thermally conductive insulating layer 1931 and to thebottom copper layer 1932.

Connections and conductors can be further protected from moisture by thesimple addition of an under fill layer of potting material or anencapsulent or an overcoat of potting material or encapsulant 1924.Potting compounds or conformal coatings are commonly used in theindustry to provide this type of protection. This type of connector isparticularly suitable for these coatings because it is essentially flatwith no recesses or areas which must be protected from contact with thecoatings.

The material chosen for the electrical insulating layer 1931 enhancesthermal conductivity. In one embodiment the electrically insulatinglayer 1931 was chosen as a high temperature variant of FR4 fiberglasswith a glass transition temperature of 170° C., although other materialscan be used. A higher than normal temperature rating of the material isintentionally used to gain more thermal margin allowing for the veryrapid heating (and probable overheating during manual assembly) of thethin boards due to their low thermal mass. Even higher temperaturematerials would be helpful in the case higher melting temperaturesolders are to be used. It is helpful to use an insulating layer 1931both durable at high temperatures and as highly thermally conductive aspossible for this construction. Thermal conductivity is helpful for thecases of solder iron or point heat source assembly because it aides inrapid transfer of heat from the top side of the pads 1903 to pads 1907below.

With reference to FIG. 20A, a top view of circuit board 1901 showselectrically conductive connection pads 1903 and plated through holes1902. Conductive pads 1904 are designed to accept electronic components1913 and printed alignment mark 1917 as shown. FIG. 20B, show the bottomside of the same circuit board 1901 with additional connection pads 1907and plated through holes 1902. In this embodiment a large conductivearea 1906 was exposed to enable good thermal transfer and heat spreadingfrom top side components and circuit paths to the bottom side.Optionally, the same area could be used for additional conductive pathsand mounting of electronic components.

With reference to FIG. 21, the top side of a second circuit board 1909is shown. Electrically conductive connection pads 1908 are designed tomatch the geometry and locations of the bottom side connection pads 1907of circuit board 1901. Electrical components may be optionally mountedat exposed conductive pads 1904 on this circuit board. In thisembodiment an alignment mark 1911 is printed on top of the solder mask1905.

With reference to FIG. 22A, a fully assembled circuit board 1912 isshown with electronic components 1913 including LED's 1914 mounted ontothe board.

With reference to FIG. 22B, two fully assembled circuit boards 1912,1916 are joined together. The lower circuit board 1912 alignment mark1911 is used to align the edge 1915 of the upper circuit board 1916 sothat the connection pads 1908, 1907 are in alignment. The upper circuitalignment mark 1917 is used to align the edge of the lower circuitboard. It is recognized one or both of these alignment marks may be ofdifferent shapes or forms or omitted in the joining process. It is alsorecognized mechanical alignment devices may be used including toolingholes, slots and sighting holes. However, in this embodiment, theinventors chose linear marks for simplicity and for visual verificationof alignment accuracy.

The circuit boards can be overlapped for interconnection (see FIG. 22B,FIG. 23). This is very useful if the connector board contains activecircuitry and it is beneficial to connect multiple boards, such as inthe fabrication of arrays of boards (see FIG. 28). The overlappingconnections are highly advantageous to the assembly of strips consistingof multiple circuit boards (see FIG. 31C). In a practical application,they are used to make long circuit board strips or arrays of solid-statelighting circuits (e.g., high power LED emitters used as the individuallight sources).

Thin board substrate materials and thicknesses are chosen to handlesolder melt temperatures without delamination or damage. Alternatechoices for board insulating material are possible such as Thermagon™ incases where higher temperature resilience and higher thermalconductivity are needed. An embodiment was developed for use with lowertemperature solders (e.g., leaded). Copper pads 1907 on the bottom sideof the upper board 1901 are designed to match the pads of the bottomreceiving board 1908 in spacing, in area and in thermal characteristics.

With reference to FIG. 23, a side profile view of an overlapping jointbetween boards in an embodiment of the present invention is shown. Inthis embodiment a connection 1919 is made by either welding or solderingthe conductive pads 1907 from the top board 1916 to the bottom boardconductive pads 1908 on the bottom board 1912. The size of pads 1907,1908 factors into both the quality of the connection and the mechanicalstress the connection can sustain. Also, by embedding or closelyconnecting through holes 1902 to pads 1907, 1908 the mechanicalperformance is improved. The metal plating and optional solder fillthrough holes 1902 links the top side pads 1903 to bottom side 1908making the bottom side very difficult to pull off (delaminate) from theinsulating layer 1931. In the embodiment, holes of 0.036 inch diameterare used to promote heat transfer, conduct solder and add enoughstructure to strengthen the joint. Lapped joints add strength by addingadditional contact area, by reducing leverage, and by changing certainforces from shearing and tensile to compressive.

The interconnect aspect of FIG. 23 allows for the coupling of circuitboards without a connector or any other device between them.

Plated through holes 1902 located at pad positions 1903, 1907 throughcircuit board 1916 allow solder and heat to flow down into theconnection both to facilitate solder connection and to enable rapidconnection. The rate of heat transfer being increased by this structurehas the additional benefit of speeding up solder melting and coolingboth during manual soldering and reflow processing. This saves time andresults in better, more repeatable and stronger joints. It is known inthe industry faster cooling times result in stronger, more uniformsolder joints.

Thin circuit boards can be easily mechanically formed for vertical stepoffsets 1921. In experiments run on these boards, bends up to a rightangle could be performed with the conductors (or any foils crossing thebend) on the inside radius of the bend.

The application of tape or adhesive 1923, across the bottom side ofjoint 1920, further increases joint strength for handling. Viscous tapesact as a spring and dampener to certain stresses, moving forces awayfrom the joint. The application of potting material 1924 or otheradhesives or coatings of structure adds additional strength to joint1920 as well as protection from mechanical damage and/or moisture (seeFIG. 24).

The application of tape or adhesive 1923 on the bottom side of the boardassembly 1922, allows the assembled strip or array to be directlyfastened to a chassis, enclosure, or heat sink 1918 without the use ofmechanical fasteners. In applications for high power LEDs it isparticularly useful to have the tape or adhesive be highly thermallyconductive so heat can easily flow from the circuit boards to the heatsink 1918. In one embodiment, a thermally conductive adhesive tape(e.g., 3M™ product #8810) was applied to the back side. The boardassembly 1922 can then be adhered to a heat sink 1918. The resultingstructure maintained excellent heat transfer to the heat sink, which isparticularly helpful in high brightness LED applications.

Intimate contact between metal pads with minimal fill layer of solderincreases strength for joint 1919. A thick layer of solder decreasesstrength but adds some flexibility to the joint. Solder has generally amuch lower tensile and shear strength than the conductors it joins.Further, solder tends to have a course crystalline structure and issusceptible to fracturing. A thin layer of solder between copper pads(used the pad material) is much less susceptible to fracturing bothbecause of smaller (or incomplete) crystal formation, and becausestresses are transferred locally to the stronger copper, instead of intothe solder itself.

A number of experiments were conducted to determine solder wetting andflow paths for various pad geometries using the thin connectors insurface mount applications. After it is melted, solder tends to wet tothe metal pads 1903 and exposed conductors of printed circuit boards1901 and 1909. It moves by capillary action to actively fill small gapsand spaces between pads 1907 and 1908, particularly pads in flatsurface-to-surface contact. If solder was applied in exactly the correctamount, the solder would simply fill the joints. But even in smallexcess, the solder would press outside of the pad areas promoting shortsand lower electrical isolation. Holes, recesses or pockets between thepads were tried and did take up the excess solder. However, the approachwas to design in plated holes 1902 within the area of the pads 1903 and1907 taking up the solder through capillary action, effectively pullingexcesses into rather than out of the joint. In the embodiment, the holeswere approximately 50% of the diameter of the pad, giving ample room forsignificant variances in solder application.

As a further improvement, plated holes 1902 can be used as receptaclesfor solder paste so boards 1912, 1916 could be ready for joining by heatalone. Flux and activating resins, which are commonly incorporated intosolder paste, are needed for high quality solder joints. In oneembodiment, the same plated holes 1902 absorb excess solder used tostore solder prior to thermal joining. Further, it is recognized theholes can be filled with either solder paste or separated layers of hardsolder and flux resin. In one experiment, solder wire with a core offlux resin was press fit in holes 1902 and sheared to match the bottomsurface plane of the circuit board 1901. This was another effective wayof putting solder and flux into plated holes 1902. Sealing of solderpaste in holes 1902 at pad positions 1903 and 1907 is helpful so pasteremains fresh for later use. Sealing may include a thin solder layer, athin flux layer or a thin plastic or metallic peel-off material.

The thin circuit board as described is flexible enough to conform tonormal variations of board thickness, solder height, and mechanicalmounting height differences. Goals for high reliability connectionsinclude robustness, both in mechanical strength and in integrity of theelectrical connection. Several designs and methods were explored andfound to improve both mechanical strength, and in many cases to improvethe electrical connection integrity. By increasing the number of pads1903, 1907 and 1908 used in the connector, mechanical strength wasbenefited. Simple multiplication of the number of contacts added to thestrength by spreading stress across the added contacts. Redundantparallel contacts reduce electrical resistance and add to the generalintegrity of electrical connection.

Increasing the size of the pads 1907 and 1908 increases the strengthboth because of the larger solder contact area, but also because of thelarger areas of contact and adhesion between pad and insulatingsubstrate. In multiple trials, larger pads consistently increased thestrength as measured in pull tests and in bending tests. Larger areas ofconductor surrounding exposed soldered pad apertures increase thestrength both by offering more area for adhesion between the conductorand the insulating substrate, but also because they add to the conductorstructure.

Increasing the distance across a set of pads or span increases the jointstrength against shear and rotational forces and torques. Shear androtational forces (torques) are common during handling of the joinedboards. Of particular use, the assembly of multiple boards into longstrips presents the opportunity to put very high torques on the jointconnection because of the length and lever arm advantage. Preventingdamage due to rotational forces is helpful to having reliable jointswhen the strips are packaged and used in their multiple forms includingstrips and continuous reeled lengths.

By increasing the distance of the pads from the overlapping edges of theboard, the inventors have found a decreased leverage on the individualconnections by converting stresses into surface pressures away from thejoint. By increasing the number of holes 1902 leading from top surfaceto the pads below, an increase in the strength is discovered by addingmore copper cylindrical connections and rivet like columns of solderfill linking top to bottom. Increased number of holes also increases theprobability of having a better percentage of solder fill between theboards. The choice of solder type and composition can have a directimpact on joint strength. Lead baring solders have lower tensilestrength then their lead free counterparts. Higher tensile strengthincreases the fracture strength of the connection.

Angled or other geometric patterns in the connection pad and copperconductors support connections for offset or angled printed circuitboards. Multiple pad sets and associated conductor connections allowsplitting of conduction paths.

As part of the printed circuit board fabrication process, mask coatingscan be placed over top of circuit boards and the bottom of circuitboards (open at the pads), reducing the opportunity for solder shortsand improving the appearance of the connector or overlapping joint. Inthe embodiments, the mask coating 1905 was chosen to match the color andcharacteristics of the boards being jointed so to minimize thevisibility of connection 1920.

In the areas of board overlap, excluding the conductive pad locations,adhesive applied between top and bottom board can be added to increasejoint strength. The board connections with overlapping joints can beused to construct elongated strips or arrays of multiple circuit boards(see FIG. 28 and FIG. 31C). Mass parallel construction of long circuitboard strips carrying high intensity LEDs for SSL applications has beenachieved using these connection types.

With reference to FIG. 25, a side profile view of a board to boardconnector joint is shown in an embodiment of the present invention. Thincircuit boards 1912 and 1916 make connection 1920 with an overlappingjoint. The circuit boards and connection are flexible enough to conformto normal variations of board thickness, solder height and mechanicalmounting height differences in many applications. In this embodiment,board to board connection is shown to bend with a radius 1925 of lessthan 1 inch. The circuit boards are adhered to a heat sink 1918 bydouble sided thermal adhesive tape 1923, affecting a permanent andhighly thermally conductive bond. The inventors have conceived ofseveral other methods of attachment, including liquid adhesives, solderor welded bonds, mechanical fasteners, and spring tensioning. In highpower LED applications, it is particularly helpful to have a goodthermal connection to the heat sink because lower LED devicetemperatures improve brightness, efficiency and increase the expectedlife.

With reference to FIG. 21A, an alternate embodiment is depicted placingthe location of connection away from the end of the board. The layeredconstruction of the circuit board has been described (see FIG. 19).Conductive pads 1903 are shown with plated through holes 1902 which passthrough to pads 1907 on the underside of the board 1926. Printedalignment marks 1929 provide guidance for connecting overlapping boards.The circuit board may be pre-assembled with electronic components, suchas LEDs 1914 and associated drive components. FIG. 26B shows theunderside of the circuit board 1926. The plated through holes 1902provide electrically conductive paths from the pads 1903 at the top ofthe board to pads 1907 at the bottom. Thermally conductive pads 1906 maybe etched or formed into the lower conductive layer enabling heat tobetter transfer and spread from the conductors, pads and components atthe top of the circuit board. The bottom side pads 1907 may beelectrically isolated from the thermally conductive pads 1906.

FIG. 26C shows the top side of another circuit board 1927 in thisembodiment connecting to the circuit board 1926. Electrically conductivepads 1908 are designed to receive connection from the previouslydescribed board. Additional alignment marks 1928 are used to guide inthe assembly of the two boards.

With reference to FIG. 27, two circuit boards 1926 and 1927 are joinedat a right angle. Alignment marks 1928 from the lower circuit board areused to locate the second circuit board squarely providing verticalguidance. Alignment marks 1929 from the upper circuit board 1926 alignto the edges of the lower circuit board 1927, providing horizontalguidance. As described earlier, solder or welding may be used to jointhe two boards forming a reliable joint 2000, forming electricalconnections between circuitry of the two boards.

The inventors conceive circuit boards may be joined at any angle and atany location within the circuit boards in accordance with thisinvention. Further, there are no limits to the number of locations andthe number of circuit boards joined.

With reference to FIG. 28, additional connections are made allowing theconstruction of a two board by two board array 2001. The connectionjoint 2000 is repeated four times in this embodiment. Additionalconnection pads 1908 and 1903 are indicated at the ends of the boardsthat can be used for connection to other boards or arrays.

The construction of circuit board arrays in accordance with thisinvention are particularly useful in SSL lighting applications becausethey reduce or eliminate wire and mechanical connector attachments andallow LEDs to be placed in specific geometric patterns without requiringas much printed circuit board material be used.

With reference to FIG. 29, construction of larger arrays and grids usingbuilding block arrays and circuit boards is conceived. In thisembodiment, multiple two by two circuit board arrays 2001 are connectedto form a larger area array.

With reference to FIG. 30, an alternate embodiment of an array iswrapped around a cylindrical drum 1943. In this embodiment, elongatedcircuit boards 1941 are joined to additional circuit boards 1944wrapping around the cylinder 1943. The individual boards are joined atconnection joints 1942 similar to those already described.

Circuit boards of various shapes and sizes may be joined to create awide variety of two and three dimensional arrays. The connection designsand methods conceived in the present invention makes it possible toassemble geometries and shapes of circuit board arrays distributingelectronic devices and circuits spatially and enable them to bepositioned and aimed for optimal effectiveness.

An aspect of the utility of constructing strips and arrays of circuitboards is the ability to shape them to size immediately prior toinstallation in a chassis or housing. Long strips and large arrays arepreferable for shipment and stocking purposes, but it is highlydesirable to be able to cut these into smaller strips and arrays fittingthe fixtures and devices they are used in. The inventors have conceiveda system of marking boards, strips and arrays to indicate safe locationsfor cutting. Further, the thin circuit board embodiments described abovecan be easily cut with simple shears or scissors 1937 (or any of avariety of tools or cutting processes).

With reference to FIG. 31A, a printed line is used to mark a safelocation for circuit separation. Conductor patterns 1935 etched into theconductive layers of the circuit boards are used to provide power andinterconnect electronic components 1913 such as LEDs 1914. At locationsdesigned in the circuit cut marks 1933, 1934 indicate the safe locationsfor separating interconnected circuits. In one embodiment, the circuitis continuous through the intended cut location. Signal conductors ortraces passing power and optionally control signals will be cut at thesame time as the boards or arrays are separated.

In order to minimize conductor damage and to minimize the opportunityfor short circuits, circuit traces are narrowed at in the immediate area1936 of the cut marks 1933. Further, the narrower traces are easier tocut because they offer less mechanical resistance. In oneimplementation, 2 oz. copper conductors were used with a width of 0.030inches in the area of cut. Outside of this area conductors are expandedto improve their current carrying and thermal conduction capability.Outside of this area are additional components and conductors whichcould be damaged and are not intended to be cut or stressed in thecutting process.

It is recognized by the inventors there may not be conductors spanningthe cut marks. There may be one or more power conductors, and one ormore control signals spanning the locations for cut.

With reference to FIG. 31B, a double line cut mark 1934 is shown. Thedouble line cut mark 1934 has the advantage of showing the boundaries ofthe safe location for cutting the board or array. The inventorsrecognize other ways for indicating safe cutting area including dottedlines, areas of grey or colored printing, tick marks and hatch markscould be used.

With reference to FIG. 31C, circuit separation utilizing the cut marksis achieved with a simple scissors or shear 1937. A long strip 1940 orarray is separated into two parts with one part 1939 being of desiredlength, size, and shape for final installation, and the second part 1938either being the residual or another part ready for final installation.

The inventors conceive the cutting of strips or arrays assembled frommultiple circuit boards may be conducted before or after the addition ofelectronic components onto these boards. Further, additional connectionsand wiring may be needed to complete the assembly. Also, after cutting,the resulting boards, strips, or arrays may again be assembled intoother shapes and combinations using the connection designs describedabove.

It can be advantageous to construct long continuous circuits for use inlinear lighting systems or other configurations constructed from linearstrip systems. While certain methods can provide for the creation oflong linear SSL circuits through manual soldering, these methods do notaddress how to build long continuous strips utilizing conventionaltechniques and equipment such as reflow soldering or wave solderingequipment.

While the soldering of individual electronic components onto circuitboards is readily accomplished with reflow or wave soldering equipment,the soldering together of individual or panelized circuit boards to eachother using this same equipment and standard techniques is not easilyaccomplished for a number of reasons.

First, the solder connection of individual or panelized circuit boardsto each other using conventional reflow or wave soldering equipment andtechniques requires that the boards be held in some fashion throughoutthe entire soldering processes. The method and apparatus for holdingneeds to provide for adequate contact between the boards to allow theheated solder to flow and wet between the boards and intended solder padareas.

The holding method and apparatus must also not interfere with theheating of the boards and solder paste material. Methods or apparatuslaid directly on top of board solder joints would tend to interfere withheat flow to the solder joints resulting in incomplete to weak solderjoints. Apparatus constructed from materials affected by the liquidsolder would tend to interfere with the solder joint or become trappedas part of the joint interfering with the quality of the joint.

The holding method and apparatus also needs to provide adequatealignment of the circuit boards in order to maintain the relativeposition of solder pads through the entire process. Wave solderingapproaches where waves of molten solder are passed over the boards isalso particularly challenging for maintaining alignment. Reflowsoldering techniques present challenges in alignment as the solderpasted circuit boards moving down a conveyor can be easily knocked outof position if simply laid onto of one another. Apparatus placeddirectly on top of boards would tend to interfere with heat flow andlimit visual inspection of solder joint quality. Heating profiles alongthe conveyor along with the flow of solder present further challenges asparts move and change shape due to thermal expansion and contractionduring heating and cooling through the reflow heating cycle along theconveyor. Parts would also need to be held from movement due to changesin surface tension as solder flux is heated and the liquid solder flowsout over the board and throughout the intended solder joint. Soldercooling from liquid to solid in the later stages of the reflow heatingcycle would further add force and movement to boards.

It would be further advantageous if the holding method and apparatus didnot interfere with visual inspection of solder joints whether manual orautomated. Large or opaque clamping apparatus would tend to prevent anyvisual inspection of the solder joint complicating inspection andquality control. Additionally, it would be advantageous that the holdingmethod be removable so as to not interfere with the end use of theresulting electronic circuit.

Embodiments herein include a method for creating long and longcontinuous circuit strips utilizing reflow or wave solder processingequipment and techniques. Further included are methods for holding aplurality of circuit boards and an apparatus for holding a plurality ofcircuit boards together during reflow or wave solder processing for thepurpose of constructing reliable and repeatable solder joints betweenthe circuit boards.

In some embodiments a method for creating long and long continuouscircuit strips by which a plurality of bottom circuit boards and aplurality of top circuit boards are prepared with solder paste, alignedfor connection and held in place with a holding apparatus and processedthrough reflow or wave soldering process. The method disclosed addressesthe connection of populated circuit boards with solder paste andelectronic components for soldering, the connection of unpopulatedplurality of circuit boards for later population with electroniccomponents through a secondary soldering process and the connection ofpre-populated and pre-soldered plurality of circuit boards for solderingof the board-to-board connection only.

In some embodiments a method is included for holding a plurality ofcircuit boards together that provides for alignment of mating solderlocations held in position throughout a reflow or wave solderingprocess. The embodiment includes a plurality of top circuit boards (a)and plurality of bottom circuit boards (b). Top circuit boards (a)including solder pad features with plated holes through the top board atpad locations allow solder and heat to flow down into the connectionboth to facilitate solder connection and to enable rapid connection.

The method of holding applies a downward force on top of a preparedjoint near the intended solder location point and an opposing downwardforce on the bottom of a prepared joint directly below the intendedsolder location. The forces are separated by a short distance and resultin a moment force at the prepared solder joint connection. The appliedforces and resulting moment force create sufficient friction forcebetween the top and bottom circuit boards to resist movement due tolateral or longitudinal forces typical in reflow or wave soldering andare therefore sufficient to maintain alignment of the top board andbottom board pad locations throughout the process.

Some embodiments herein are directed to an apparatus for holding aplurality of circuit boards together to provide for alignment of matingsolder locations held in position throughout a reflow or wave solderingprocess. The apparatus in some embodiments is in the form of a circuitboard clamp. The circuit board clamp can include a fastener, such as au-shaped fastener, to apply pressure to a plurality of top circuitboards and bottom circuit boards. The circuit board clamp can alsoinclude a spring tension arm connected to the u-shaped fastener. Inaddition, an attachment mechanism can be connected to the spring tensionarm on the opposite end from the fastener. The attachment mechanism canserve to provide attachment to the lower circuit boards. In someembodiments, the attachment mechanism is a hook. The spring tension armcan provide spring force between the fastener end and the attachmentmechanism.

In some embodiments, a method for creating long and long continuouscircuit strips utilizing reflow or wave solder processing equipment andtechniques is included. Further included are methods for holding aplurality of circuit boards and an apparatus for holding a plurality ofcircuit boards together during reflow or wave solder processing for thepurpose of constructing reliable and repeatable solder joints betweenthe circuit boards.

With reference to FIG. 32, a schematic top view of two circuit boardsconnected with a connector in an embodiment is shown. Circuit boards3205 and 3206 are shown joined with connector board 3202 to create LEDcircuit 3300. While the embodiment shown in FIG. 32 is directed towardsflexible lighting circuit boards and more directly towards flexible LEDcircuit boards, it will be appreciated that the scope of embodimentsherein are not limited to flexible lighting circuit boards and caninclude many different types of circuit boards.

While connector board 3202 is shown coupling the top surfaces of circuitboards 3205 and 3206 it is fully contemplated connector board 3202 couldbe coupled between circuit boards 3205 and 3206 in most any fashionincluding on the bottom surface of circuit boards 3205 and 3206 andoverlapping between a top surface and a bottom surface. Circuit boards3205 and 3206 are shown with component pads 3204 for receiving LEDs orother components. Connector board 3202 has plated through holes 3201disposed in conductive metal pads 3227. Plated through holes 3201 allowsolder to flow through to connect circuit boards 3205 and 3206 as willbe discussed in more detail below.

With reference to FIG. 33, a top profile view of a connector board in anembodiment is shown. Connector board 3202 consists of a thin circuitboard 3400 comprised of two electrically conductive layers 3402 with athin electrical isolating material 3404 sandwiched in between. In someembodiments, the conductive layers can be made of a conductive metal invarious thicknesses. By way of example, in some embodiments, theconductive layers can be made of copper. In a particular embodiment, theelectrically conductive layers are 2 oz. copper. It will be appreciatedthat many different materials can be used for the electrical isolatingmaterial. Such materials can have various thicknesses. In someembodiments, the electrical isolating material can be fiberglass. In aparticular embodiment the electrical isolating material is 0.012 inchthick fiberglass composite material.

Circuit paths 3210 of various designs can be etched into the top and/orbottom conductive layers to produce the circuit conductive paths. Platedthrough holes 3201 can be added at metal pads 3227 and plated throughwith conductive metal to form a connection between top and bottom. Thinlayers of non-conductive solder repelling material 3211 (solder masks)can be added to the top and bottom of the board to restrict the movementof solder and protect the circuit paths from the pads.

With reference to FIG. 34, a top profile view of an outline of a routedpanel ready for component assembly and cutting in an embodiment isshown. Panels 3302 of thin, flexible printed circuit boards can befabricated and routed so there is some amount of material 3212 remainingto keep multiple parallel boards 3213 in a parallel array. The material3212 outside of the circuit board array further stiffens panel 3302 andmay contain alignment marks or tooling holes for mechanical handling andalignment. Tabs 3216 in a repeating pattern can be used to hold circuitboards 3213 together. Routed slits 3214 between tabs 3216 can be used tomaintain mechanical alignment during assembly.

Panels 3302 can be configured to allow them to be cut with aconventional shear, scissors, or other cutting device at any of severallocations enabling later trimming to length or separation. It is fullycontemplated panels 3302 could be laser cut as well to obtain circuitboards 3205 and 3206. Circuit boards 3205 and 3206 can be part of panels3302 as indicated by circuit board location 3213. Electrical components,including LED emitters and optionally thin board connectors can beassembled onto panels 3302 by conventional methods of electronic solderassembly. In some embodiments, the connector pad geometry can beincorporated into the board design so an additional connector board isnot required, rather circuit boards 3205 and 3206 can be directlyfastened together.

With reference to FIG. 35, a top profile view of a panel outline withends sheared off to expose boards is shown in accordance with anembodiment. As shown, sheared panel 3303 frees up one or both ends 3306and 3304 of each printed circuit board 3213. In some embodiments, thiscan be done during the original panel fabrication. In some embodiments,a portion of the frame 3219 may be retained to add stiffness to theassembly and may contain alignment marks and tooling holes used tomaintain mechanical alignment during assembly.

With reference to FIG. 36, a top profile view of panels joined byconnectors in an embodiment is shown. A free end 3304 of one panel canbe butted against a free end 3306 of the other so several circuit boardscan be joined by soldering or welding, thus forming a longer assemblywith the same characteristic of parallel strips. Depending on desiredlength, the process can be repeated by adding additional panels 3303 toan elongated panel made up of multiple panels 3303. After the desiredlength is attained, the strips can be separated by shearing anyremaining connecting material. As the long strips are joined, linedthermal adhesive tape 3228 (FIG. 39) can be affixed to the bottom of thestrips in a continuous action. The exposed liner (not shown) can belater removed during application of the joined strips to a fixture orpermanent mount. The addition of thermal adhesive tape 3228 can occurjust before or after panels 3303 are joined together. The resultingelongated strips can then be wound onto large diameter reels so they canbe easily protected, transported, and stored; ready for final assemblyonto heat sinks or light fixtures. As an alternative, the strips can beshort enough to be packaged and shipped in flat form.

With reference to FIG. 37, a top profile view of circuit strips afterseparation in an embodiment is shown. As shown, circuit strips 3220 canbe separated from panels 3303. Connection point 3221 connecting two ormore circuit strips can be a connector 3202 as discussed above or anoverlap joint discussed in more detail below. LEDs 3222 or othercomponents can be adhered or placed on circuit strips 3220 and circuitstrips 3220 can terminate at ends 3223.

With reference to FIG. 38, a top profile view of soldering of aconnector joint in an embodiment is shown. Connector board 3202 can beflexible enough to conform to normal variations of board thickness,solder height and mechanical mounting height differences. In anembodiment, connector board 3202 is shown to bend with a radius 3242 ofdown to 1 inch (see FIG. 45). The connector board 3202 can allow heatand solder to easily flow through connector board 3202 from top tobottom as heat is applied. Solder may be introduced into through hole3201 at the top of connector board 3202. Alternatively solder may be inpaste or hard form deposited on receiving printed circuit board 3205 or3206, in which case solder will flow from bottom to top.

Electrically insulating layer 3404 within the thin board is thin enoughto both enable a high degree of thermal conductivity and is able tomaintain high levels of electrical breakdown isolation. Electricalisolation between circuits is helpful to the general function of theconnector; however, the amount of isolation may be changed to conform tothe application requirements.

The material chosen for the electrical insulating layer can enhancethermal conductivity. In one embodiment the electrically insulatinglayer was chosen as a high temperature variant of FR4 fiberglass with aglass transition temperature of 170° C., although this is just oneexample and many other materials can be used. A higher than normaltemperature rating of the material can be used to gain more thermalmargin allowing for the very rapid heating (and probable overheatingduring manual assembly) of the thin boards due to their low thermalmass. Even higher temperature materials can be used in the case highermelting temperature solders are to be used. In some embodiments, theinsulating layer is both durable at high temperatures and as highlythermally conductive as possible for this construction. Thermalconductivity can be helpful for the cases of solder iron or point heatsource assembly because it aides in rapid transfer of heat from the topside of the connector to the joints below.

Thin connector 3202 board can add flexibility to connection 3221,reducing stress at the solder joint associated with the use of rigidpins and other types of connectors. This is helpful to prevent tearingof the printed circuit board pads on the board when bending stresses areintroduced. In one implementation, connector boards 3202 can be used toform a continuous strip of boards which is then rolled into reel form.The bend radius 3242 of this implementation can be 6 inches or greater.

Thin board substrate materials and thicknesses can be selected to handlesolder melt temperatures without delamination or damage. Alternatechoices for board insulating material can include materials such asTHERMAGON™ thermally conductive materials in cases where highertemperature resilience and higher thermal conductivity are needed. Anembodiment was developed for use with lower temperature solders(leaded). Copper pads 3231 can be on the bottom side of the connector orupper board and can be designed to match the pads 3233 of the receivingboard—in spacing, in area, in thermal characteristics.

With reference to FIG. 39, a side profile view of an overlapping jointbetween boards in an alternate embodiment is shown. In the embodiment ofFIG. 39 no connector board 3202 is used to connect circuit boards 3205and 3206. The bottom side of an end of circuit board 3206 is directlyconnected to the top side of an end of circuit board 3205. Conductivemetal pads 3227 can be on the top side to receive heat (such as from asoldering iron 3224, shown in FIG. 38) and provide a path for conductionthrough the electrically insulating substrate and/or a plated throughhole 3201 to conductive metal pads 3233 (shown for example in FIG. 43)on the bottom. The size of pads 3230, 3231 and 3233 (FIGS. 42A, 42B and43) factor into both the quality of the connection and the mechanicalstress the connection can sustain. In some embodiments, by embedding orclosely connecting through holes 3201 to pads 3231, 3238, the mechanicalperformance can be improved. The metal plating and solder fill throughhole 3201 links top side pads 3227 to bottom side pads 3233 making thebottom side very difficult to pull off (delaminate) from the insulatinglayer. Through holes can be of various sizes. In some embodiments, thethrough holes can be about 0.036 inches in diameter to promote heattransfer, conduct solder and add enough structure to strengthen thejoint. Lapped joints add strength by adding additional contact area, byreducing leverage, and by changing certain forces from shearing andtensile to compressive.

The interconnect aspect of FIG. 39 allows for the coupling of circuitboards without a connector board or any other device between them. Thuscircuit boards 3205 and 3206 can be created with ends 3304 and 3306which have pads 3230, 3231 and 3233 with though holes 3201 to allowcoupling of the circuit boards.

Copper conductors can be used for connecting pads 3227 to be mated tocircuit path 3210. Circuit path 3210 can be printed in almost anypattern, such as those commonly used in circuit boards and can bepatterned to receive electronic components such as LEDs 3222, integratedcircuits 3236, or other electronic components. In some embodiments, thecopper conductors can be very thick and wide to accommodate highcurrents. In a particular embodiment 2 oz. copper was used with aconductor width of 0.040 inch to enable a low voltage drop across theconnector when carrying up to 3205 amps of current.

Copper foils are designed to maintain gap distances between connectionsfor electrical isolation. In an embodiment, voltage isolations of up to500 V were maintained by maintaining a distance of 0.025 inches betweencopper foils. By increasing the spacing, substantially higher isolationscan be achieved. Copper conductors can be run on top of or under theconnector insulating substrate, depending on requirements for isolation,current carrying capacity and protection. Connections and conductors areprotected from damage or shorting by being covered by the connector bodyor overlapping joint 3226.

Connections and conductors can be further protected from moisture by thesimple addition of an under fill layer of potting material or anencapsulent or an overcoat of potting material 3229 or encapsulent.Potting compounds or conformal coatings are commonly used in theindustry to provide this type of protection. This type of connector isparticularly suitable for these coatings because it is essentially flatwith no recesses or areas which must be protected from contact with thecoatings.

Plated through holes 3201 located at pad positions 3227, 3230 and 3231through connector board 3202 allow solder and heat to flow down into theconnection both to facilitate solder connection and to enable rapidconnection. The rate of heat transfer being increased by this structurehas the additional benefit of speeding up solder melting and coolingboth during manual soldering and reflow processing. This can save timeand result in better, more repeatable and stronger joints.

A number of experiments were conducted to determine solder wetting andflow paths for various pad geometries using the thin connectors insurface mount applications. After it is melted, solder tends to wet tothe metal pads 3230 and exposed conductors of printed circuit boards3205 and 3206. It moves by capillary action to actively fill small gapsand spaces between pads 3231 and 3233, particularly pads in flatsurface-to-surface contact. The high degree of adhesion and capillaryaction exhibited by solder, combined with the mechanical weight of thethin board connector caused pads of connector board 3202 and circuitboards 3205 and 3206 to pull together pushing remaining solder outwardbetween pads 3231 and 3233. If solder was applied in exactly the correctamount, the solder would simply fill the joints. But even in smallexcess, the solder would press outside of the pad areas promoting shortsand lower electrical isolation. Holes, recesses or pockets between thepads were tried and did take up the excess solder. However, the approachwas to design in plated holes 3201 within the area of the pads taking upthe solder through capillary action, effectively pulling excesses intorather than out of the joint. In a particular embodiment, the holes wereapproximately 50% of the diameter of the pad, giving ample room forsignificant variances in solder application. Though it will beappreciated that other hole size to pad diameter ratios can be used.

In some embodiments, plated holes 3201 can be used as receptacles forsolder paste so connectors 3202 could be ready for joining by heatalone. Once aligned to printed circuit boards 3205 and 3206, connector3202 (or selectively its pads) can be heated to cause the solder tobegin melting for example using a soldering iron 3224. By capillaryaction and wetting, the solder quickly flows down into the space betweenconnector 3202 and board pads completing the joint. Flux and activatingresins, which are commonly incorporated into solder paste, are neededfor high quality solder joints. In one embodiment, the same platedthrough holes 3201 used to store solder prior to thermal joining absorbexcess solder. Further, the holes can be filled with either solder pasteor separated layers of hard solder and flux resin. In one embodiment,solder wire with a core of flux resin can be press fit in holes 3201 andsheared to match the connector bottom surface 3226. It wasexperimentally determined that this was another effective way of puttingsolder and flux into plated holes 3201. Sealing of solder paste in holes3201 at pad positions 3227 and 3226 can be helpful so paste remainsfresh for later use. Sealing can include a thin solder layer, a thinflux layer or a thin plastic or metallic peel off material.

As part of the printed circuit board fabrication process, mask coatings3211 can be placed over the top and the bottom of the connector board(open at the pads), reducing the opportunity for solder shorts andimproving the appearance of the connector or overlapping joint. In someembodiments, the mask coating can be chosen to match the color andcharacteristics of the boards being jointed so to minimize thevisibility of connector board 3202. Connector board 3202 can beimplemented without mask coatings on the top surface as this is lesscritical to the solder flow protection function.

Connector boards 3202 can be easily mechanically formed for verticalstep offsets 3241. In experiments run on these connectors 3202, bends upto a right angle could be performed with the conductors (or any foilscrossing the bend) on the inside radius of the bend.

Connector boards 3202 can incorporate other circuits, including pads andgeometries for wire or other conventional types of connectors, as wellas being able to incorporate terminations and active circuitry.Connector board 3202 is particularly well suited because of its highlythermally conductive structure for power and heat creating circuits. Inone implementation, the circuitry included a high current driver (OneSemiconductor #NUD4001 operating at 3224 VDC) along with an LED stringadded to the top side of the board. Both the top (FIG. 42a ) and bottomside (FIG. 42b ) of the board were designed with large metal (such ascopper) pads 3230 and 3231 that could translate heat through the thininsulating material by effectively creating a large area for heattransfer from the top copper layer through the less thermally conductiveinsulating layer and to the bottom copper layer. Further, a thermallyconductive adhesive tape 3228 (e.g., 3M product #8810) can be applied tothe back side. The assembly can then be adhered to a heat sink 3225. Theresulting structure was found to maintain excellent heat transfer to theheat sink, which is particularly important in high brightness LEDapplications.

Because this connector can be easily fabricated in many shapes, it canbe used for connection between boards directly abutted (FIG. 36) or somedistance apart. Also, since the conductors can be on either top orbottom, or embedded in a center layer, electrical isolation fromneighboring structures can be high and possible shorting points can bereadily avoided. Connector boards 3202 are stackable and can be solderedone to another.

In cases where additional mechanical support is needed, the connectorcan extend well beyond the pad providing maximum overlap. It may benecessary to shape the connector or have it fabricated with clearanceholes if components on the underlying board may interfere. Connectorboard 3202 can be fabricated with additional pads and holes (notconnected to the circuits) to give additional strain relief. Padgeometries may match existing pinned connectors to allow the option toalternate use of a pinned connector or thin board connector. Thinconnector boards may be used to join circuit boards into strips 3220 ormatrixes with multiple connectors or connections 3221 in each assembledlength (See FIG. 37).

Thin connector boards can be overlapped for interconnection (See FIG.39). This is very useful if the connector board contains activecircuitry and it is beneficial to connect multiple boards, such as inthe fabrication of a continuous strip of boards (See, e.g., FIG. 37).The thin connector boards can be highly advantageous to the assembly ofstrips consisting of multiple circuit boards (See FIG. 40). In apractical application, they can be used to make long circuit boardstrips of solid state lighting circuits (e.g., high power LED emittersused as the individual light sources), amongst other applications.

Thin circuit board 3213 can include a thin, low thermal mass substratebase material comprised of two electrically conductive layers with athin, electrically isolating material sandwiched in between. In someembodiments, the conductive layers can be made of a conductive metal invarious thicknesses. By way of example, in some embodiments, theconductive layers can be made of copper. In a particular embodiment, theelectrically conductive layers are 2 oz. copper. It will be appreciatedthat many different materials can be used for the electrical isolatingmaterial. Such materials can have various thicknesses. In someembodiments, the electrical isolating material can be fiberglass. In aparticular embodiment the electrical isolating material is 0.012 inchthick fiberglass composite material. Circuit patterns of various designscan be etched into the top and bottom conductive layers to produce thecircuit conductive paths. Holes can be added at the pad locations andplated through with conductive metal to form a connection between topand bottom. Additional thin layers of non-conductive, solder repellingmaterial (solder masks) can be added to the top and bottom of the boardto restrict the movement of solder and protect the circuit paths awayfrom the pads.

Angled or other geometric patterns in the pad and copper conductors canbe included and can support connections for offset or angled printedcircuit boards. Multiple pad sets and associated conductor connectionscan be included and can allow for splitting of conduction paths.

The thin circuit board as described can be flexible enough to conform tonormal variations of board thickness, solder height, and mechanicalmounting height differences (See FIG. 45). Goals for high reliabilityconnections include robustness, both in mechanical strength and inintegrity of the electrical connection. By increasing the number of pads3230, 3231 and 3233 used in the connector, mechanical strength wasincreased. Simple multiplication of the number of contacts added to thestrength by spreading stress across the added contacts. Redundantparallel contacts reduce electrical resistance and add to the generalintegrity of electrical connection.

Intimate contact between metal pads with minimal fill layer of solderincreases joint 3226 strength. A thick layer of solder decreasesstrength but adds some flexibility to the joint. Solder generally has amuch lower tensile and shear strength than the conductors it joins.Further, it tends to have a course crystalline structure and issusceptible to fracturing. However, a thin layer of solder betweencopper pads (used the pad material) is much less susceptible tofracturing both because of smaller (or incomplete) crystal formation,and because stresses are transferred locally to the stronger copper,instead of into the solder itself.

Increasing the size of the pads 3231 and 3233 increases the strengthboth because of the larger solder contact area, but also because of thelarger areas of contact and adhesion between pad and insulatingsubstrate. In multiple trials, larger pads consistently increased thestrength as measured in pull tests and in bending tests. Larger areas ofconductor surrounding exposed, soldered pad apertures increase thestrength both by offering more area for adhesion between the conductorand the insulating substrate, but also because they add to the conductorstructure.

Increasing the distance across a set of pads 3237 or span increases thejoint strength against shear and rotational forces and torques. Shearand rotational forces (torques) are common highest during handling ofthe joined boards. Of particular use, the assembly of multiple boardsinto long strips presents the opportunity to put very high torques onthe joint connection because of the length and spring tension armadvantage. Preventing damage due to rotational forces is helpful tohaving reliable joints when the strips are packaged and used in theirmultiple forms including strips and continuous reeled lengths.

By increasing the distance of the pads from the overlapping edges of theboard, the inventors have found a decreased leverage on the individualconnections by converting stresses into surface pressures away from thejoint. By increasing the number of through holes 3201 leading from topsurface to the pads below, an increase in the strength is discovered byadding more copper cylindrical connections and rivet like columns ofsolder fill linking top to bottom. Increased number of holes alsoincreases the probability of having a better percentage of solder fillbetween the boards. The choice of solder type and composition has adirect impact on joint strength. Lead baring solders have lower tensilestrength then their lead free counterparts. Higher tensile strengthincreases the fracture strength of the connection.

The application of tape or adhesive 3228, across the bottom side ofjoint 3226, can further increase joint strength for handling. Viscoustapes act as a spring and dampener to certain stresses, moving forcesaway from the joint. The application of potting material 3229 or otheradhesives or coatings of structure adds additional strength to joint3226 as well as protection from mechanical damage and/or moisture (SeeFIG. 41).

In the areas of board overlap, excluding the conductive pad locations,adhesive applied between top and bottom board can be added to increasejoint strength. Thin board connectors 3202 or thin circuit boards 3213and 3239 with overlapping joints 3226 can be used to construct elongatedstrips of multiple circuit boards 3220. Mass parallel construction oflong circuit board strips carrying high intensity LEDs for SSLapplications has been demonstrated using these connection types.

With reference to FIG. 46, a process flow diagram for construction ofmulti-board assemblies in strip or matrix form in an embodiment isshown. Process 3500 starts at state 3502 where circuit panels 3302 arefabricated as discussed in detail above. At state 3504 components, suchas LEDs are coupled to circuit boards 3205 and 3206, which are developedfrom panel 3302. If necessary, circuit joints 3218 are exposed forassembly at state 3506. At state 3508 board panels or arrays are joinedby solder or welding. At state 3510 strip assemblies within the boardpanels or arrays are separated from each other. At state 3512 individualstrips can be joined into longer strips or matrix (including, forexample, some boards arranged perpendicularly to one another) forms.

In some embodiments a method is included for creating long continuouscircuit strips in which a plurality of bottom circuit boards and aplurality of top circuit boards are mechanically and electricallyconnected together by way of a soldered lap joint connection. Thesoldered lap joint connection results from the processing of the bottomand top plurality of circuit boards through conventional reflowsoldering or wave soldering processes.

In reference to FIG. 47, the plurality of bottom circuit boards 4101 anda plurality of top circuit boards 4102 are aligned for connection with aprepared lap joint 4117 and held in place with a circuit board clamp4116 and processed through either conventional reflow or wave solderingprocesses. The method disclosed addresses the connection of populatedcircuit boards with solder paste and electronic components forsoldering, the connection of unpopulated plurality of circuit boards forlater population with electronic components through a secondarysoldering process and the connection of pre-populated and pre-solderedplurality of circuit boards for soldering of the board-to-boardconnection only.

In some embodiments a method is included for holding a plurality ofcircuit boards together that provides for alignment of mating solderpads held in position throughout a reflow or wave soldering process. Inreference to FIG. 47, a plurality of bottom circuit boards 4101 can beplaced onto a conveyor belt or table for advancing the boards into thereflow solder oven. A second plurality of top circuit boards 4102 can isplaced on top of the first plurality of circuit boards 4101 with somearea of overlap. The placement of the circuit boards is done with careto align the plurality of solder pad features of the top circuit boards4102 with the bottom circuit boards 4101 to create a prepared joint4117.

Referring now to FIG. 48, the alignment of the top and bottom pluralityof circuit boards is such that the solder pads 4010 on the top pluralityof circuit boards 4102 are aligned with the receiving solder pad 4011 onthe bottom plurality of circuit boards 4101. Top circuit boards 4102including solder pad features previously disclosed with plated holes4025 through the top board at the pad locations. Plated holes 4025 inthe top circuit board 4102 allow solder and heat to flow down into theconnection both to facilitate solder connection and to enable rapidconnection.

Referring now to FIG. 49, the top and bottom plurality of circuit boardsmay be prepared in advance with solder paste 4012 onto the solder padsof only the plurality of top circuit boards 4102, or with solder paste4012 onto the solder pads 4010 of the plurality of top circuit boards4102 and solder pads 4011 of the plurality of bottom circuit boards4101, or with solder paste 4012 onto the solder pads 4011 of only thebottom plurality of circuit boards 4101. In some embodiments, the amountof solder paste used is controlled with precision.

Referring now to FIG. 50, the resulting soldered lap joint connection4117 provides for a reliable mechanical and electrical board-to-boardconnection for the plurality of top circuit boards 4102 and bottomcircuit boards 4101 creating a long circuit board assembly 4301 (or longcircuit board strip). The process can be repeated by adding additionaltop circuit boards 4102 to the newly created long circuit board assembly4301 to create a long continuous circuit board assembly 4302 (in FIG.54) (or long continuous circuit board strip).

In some embodiments, an apparatus is included for holding a plurality ofcircuit boards together to provide for alignment of mating solderlocations and held in position throughout a reflow or wave solderingprocess. In some embodiments, this apparatus can be a circuit boardclamp. Referring to FIG. 51, the apparatus in some embodiments is in theform of a circuit board clamp 4116 with a fastener 4118, an attachmentmechanism 4119 and a spring tension arm 4120. The fastener 4118 appliespressure to a plurality of top circuit boards 4102 and bottom circuitboards 4101. The attachment mechanism 4119 attaches to the bottom of thetop circuit boards 4102 and a spring tension arm 4120 provides springforce between the fastener end 4118 and attachment mechanism end 4119.In some embodiments, the fastener 4118 is in the form of a u-shapedfastener. The fastener 4118 can include a top bar portion 5001, a bottombar portion 5003, and an interconnection member 5005 disposed betweenthe two. In some embodiments, the top bar portion 5001 and the bottombar portion 5003 are substantially parallel to one another. In someembodiments, the spring tension arm 4120 has a major axis orientedsubstantially perpendicularly to the top bar portion 5001.

It will be appreciated that the circuit board clamp 4116 may take manyshapes in order to accommodate differing boards and connectorgeometries. The embodiment of FIG. 51 illustrates the form of thecircuit board clamp 4116 as constructed from small gauge wire. Theselection of a small gauge allows for the fastener end 4118 to easilyfit through a narrow routed slot 4121 in the bottom plurality of circuitboards 4102 and be rotated approximately 90 degrees at the intendedholding points on the top circuit board at point 4201 and on the bottomcircuit board at point 4202 on the overlapping boards (see FIG. 41). Thesmall gauge wire allows for the attachment mechanism end 4119 to passthrough the narrow routed slot 4121 in the top plurality of boards 4101.The resulting circuit board clamp 4116 provides the necessary forces asdescribed above to hold the top and bottom plurality of circuit boardsin alignment for processing through a reflow or wave solderingoperation.

A number of experiments were conducted on the circuit board clamp 4116embodiment. It was found that a reverse bend 4122 in the bottom barportion 5003 of the fastener 4118 improved the ability to hold the topcircuit board 4102 and bottom circuit board 4101 parallel to each other.The reverse bend 4122 is “reverse” in that it results in the distal endof the bottom bar portion 5003 being pointed away from the top barportion 5001 as shown in FIG. 52.

Parallel surfaces in the prepared solder joint 4117 were found toimprove solder wetting throughout the joint. Further experiments wereconducted on the attachment mechanism end 4119 of the circuit boardclamp 4116. It was found that a hook attached to the top circuit board4102 through the narrow routed slot 4121 away from the routed tabbetween boards 4123 eliminated the need for the circuit board clamp 4116to be sized specific to each board routing pattern 4121, 4123. In someembodiments, the attachment mechanism 4119 can comprise an attachmenthook 5007.

FIG. 55 is a schematic top perspective view of a plurality of circuitboard clamps 4116 holding top 4102 and bottom 4101 circuit boardstogether in accordance with various embodiments herein. In reference toFIG. 55, the method of holding involves the application of a downwardforce 4201 with circuit board clamp 4116 on the top of a prepared lapjoint 4117 of the top circuit board 4102 near the intended solder point4019, an opposing upward force 4202 on the bottom of a prepared lapjoint 4117 of the bottom circuit 4101 directly below the intended solderlocation. The forces are separated by some lateral distance resulting ina force moment at the prepared lap joint 4117 for solder connection. Theapplied forces and resulting force moment create friction force withinthe prepared joint. The resulting friction force is sufficient to resistmovement due to forces typical in reflow or wave soldering processes andis therefore sufficient to maintain alignment of the top plurality ofcircuit boards 4101 and bottom plurality of circuit boards 4102 withinthe prepared lap joint 4117. FIG. 56 is a schematic bottom perspectiveview of a plurality of circuit board clamps 4116 holding top 4102 andbottom 4101 circuit boards together in accordance with variousembodiments herein.

FIG. 57 is a schematic view of top 4102 and bottom 4101 circuit boardswith circuit board clamps 4116 illustrating how the circuit board clamps4116 allow for a visual inspection step of the through holes 4025 andsolder therein in accordance with various embodiments herein.

In reference to FIG. 58, a reflow soldering process is shown where aplurality of top circuit boards 4102 and a plurality of bottom circuitboards 4101 are held together in a prepared lap joint 4117 and placedonto a conveyor belt 4401 for feeding into reflow solder oven 4400. Theresulting reflow soldered long circuit boards 4301 and continuoussoldered circuit boards 4302 with soldered lap joints 4015 exit reflowsolder oven at conveyor belt 4402.

In reference to FIG. 59, a wave soldering process is shown where aplurality of top circuit boards 4102 and a plurality of bottom circuitboards 4101 are held together in a prepared lap joint 4117 and placedonto a wave solder machine 4410 feeder table 4411. The resulting wavesoldered long circuit boards 4301 and continuous soldered circuit boards4302 with soldered lap joints 4117 exit reflow solder oven at exit table4412.

Pre-Populated Circuit Boards

It will be appreciated that methods in accordance with embodimentsherein can be performed with unpopulated circuit boards, pre-populatedcircuit boards, and pre-populated and pre-soldered circuit boards. Byway of example, FIG. 53 shows an embodiment in which the top circuitboards 4102 and bottom circuit boards 4101 may be pre-populated withsolder paste 4012 b and electronic components 4013 as in conventionalpreparation of circuit boards for reflow or wave soldering on to thecircuit boards. The plurality of populated top circuit boards can thenbe prepared with solder paste 4012 at the solder pads 4010. Solder paste4012 may also be applied to the plurality of pre-populated bottomcircuit boards 4101 at pads 4011 although tests conducted indicated theaddition of solder paste on the bottom circuit board 4101 solder pads4011 was not necessary to achieve reliable solder joints.

The plurality of pre-populated top circuit boards 4102 can then bealigned over the top of the plurality of pre-populated bottom circuitboard 4101 solder pads 4011 and held in place with an apparatus 4116creating a prepared lap joint 4117 (see e.g., FIG. 47) ready for reflowor wave solder processing. The resulting reliable soldered lap joint4015 (see, e.g., FIG. 54) can result in a long circuit board assembly4301 (FIG. 50). The process can be repeated by adding additional topcircuit boards 4102 to the newly created long circuit board assembly4301 to create a long continuous circuit board assembly 4302 (see, e.g.,FIG. 54). An example of one method for preparation, alignment,connection, soldering and removal for pre-populated circuit boards isdescribed in FIG. 60 (identified as “Process B—Pre-populated”). It willbe appreciated that soldering can include the steps of a heating cycle,solder flow, and a cooling cycle.

The alignment of the top and bottom plurality of circuit boards is aidedthrough initial visual alignment of the solder pad 4010 to solder pad4011 and board end 4016 and board alignment marks 4014. The top andbottom circuit board alignment for solder processing is then determinedby long board edge 4018 and circuit board clamp 4116. The resultingprepared joint 4117 is aligned and held in place with circuit boardclamp 4116 for reflow or wave soldering.

Pre-Populated and Pre-Soldered Circuit Boards

FIG. 61 shows a further embodiment in which the top circuit boards 4112and bottom circuit boards 4111 both may be pre-populated andpre-soldered with electronic components 4013 soldered onto the pluralityof circuit boards. In this embodiment the pre-populated and pre-solderedtop circuit boards 4112 can then prepared with solder paste 4012 at thesolder pads 4010. Solder paste 4012 can also be added to the pluralityof bottom circuit boards 4111, but was found to not be necessary toachieve reliable solder joints. The plurality of pre-populated andpre-soldered top circuit boards 4112 are then aligned over the top ofthe plurality of pre-populated and pre-soldered bottom circuit boards4111 for soldering of the prepared lap joint 4117 (FIG. 47) ready forreflow or wave solder processing. The resulting reliable soldered lapjoint 4015 (FIG. 54) resulting in a long circuit board assembly 4301(FIG. 50). The process can be repeated by adding additional top orbottom circuit boards to the newly created long circuit board assemblyto create a long-continuous circuit board assembly 4302 (FIG. 54). Anexample of one method for preparation, alignment, connection, solderingand removal of pre-populated and pre-soldered circuit boards isdescribed in FIG. 60 (identified as “Process C—Pre-Soldered”).

Unpopulated Circuit Boards

FIG. 62 shows a further embodiment included herein where the top circuitboards 4102 and bottom circuit boards 4101 can be left unpopulated andspecifically where electrical component positions 4017 can be leftunpopulated. The plurality of top circuit boards 4102 can be preparedwith solder paste 4012 at the solder pads 4010 for creation of preparedlap joint 4117. Solder paste 4012 can also be added to the plurality ofbottom circuit boards 4101, but was found to not be necessary to achievereliable solder joints. The plurality of pre-populated and pre-solderedtop circuit boards 4102 are then aligned over the top of the pluralityof pre-populated and pre-soldered bottom circuit boards 4101 forsoldering of the prepared lap joint 4117 ready for reflow or wave solderprocessing. Referring to FIG. 63, the resulting reliable soldered lapjoint 4015 resulting in a long circuit board assembly. The process canbe repeated by adding additional plurality of top circuit boards 4102 tothe newly created long circuit board assembly to create along-continuous circuit board assembly 4312. An example of one methodfor the preparation, alignment, connection, soldering and removal ofunpopulated circuit boards is described in FIG. 60 (identified as“Process A—Unpopulated”).

Experiments conducted during reflow soldering demonstrated a pluralityof circuit boards held by an apparatus 4116 in the form of a preparedjoint 4117 (FIG. 47) could be successfully soldered together into areliable solder joint (FIG. 50) providing mechanical and electricalconnection between the top circuit board 4102 and bottom circuit board4101.

A number of experiments were previously conducted to determine solderwetting and flow paths for various pad geometries using overlappedboards in surface mount applications. After melting, solder wets to themetal pads and exposed conductors of printed circuit boards. The soldermoves through capillary action to actively fill small gaps and spacesbetween upper and lower board pads, particularly pads in flatsurface-to-surface contact as previously disclosed. The high degree ofadhesion and capillary action exhibited by liquid solder, combined withthe mechanical force moment on the prepared joint 4117 (FIG. 55)provides for reliable soldering of the top circuit board 4102 and bottomcircuit board 4101 into reliable solder joint (FIG. 50).

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the content clearly dictates otherwise. It should also be notedthat the term “or” is generally employed in its sense including “and/or”unless the content clearly dictates otherwise.

It should also be noted that, as used in this specification and theappended claims, the phrase “configured” describes a system, apparatus,or other structure that is constructed or configured to perform aparticular task or adopt a particular configuration to. The phrase“configured” can be used interchangeably with other similar phrases suchas arranged and configured, constructed and arranged, constructed,manufactured and arranged, and the like.

All publications and patent applications in this specification areindicative of the level of ordinary skill in the art to which thisinvention pertains. All publications and patent applications are hereinincorporated by reference to the same extent as if each individualpublication or patent application was specifically and individuallyindicated by reference.

The invention has been described with reference to various specific andpreferred embodiments and techniques. However, it should be understoodthat many variations and modifications may be made while remainingwithin the spirit and scope of the invention.

Further Embodiments

In some embodiments, an LED lighting system is included. The LEDlighting system can include a flexible layered circuit structureincluding a top thermally conductive layer, a middle electricallyinsulating layer, a bottom thermally conductive layer, and a pluralityof light emitting diodes mounted on the top layer. The system canfurther include a housing substrate and a mounting structure. Themounting structure can be configured to suspend the layered circuitstructure above the housing substrate with an air gap disposed inbetween bottom thermally conductive layer of the flexible layeredcircuit structure and the housing substrate. The distance between thelayered circuit structure and the support layer can be at least about0.5 mm. The system can further include a plurality of light emittingdiodes mounted on the bottom layer. The system can further include anoptically translucent material layer disposed over the top thermallyconductive layer. The distance between the layered circuit structure andthe support layer can be between about 0.5 mm and 100 mm. The distancebetween the layered circuit structure and the support layer can bebetween about 40% and 60% of the width of the flexible layered circuitstructure. The mounting structure can include a tensioner to applytension to the flexible layered circuit structure. The tensioner canprovide a spring force applied to the flexible layered circuitstructure. The tensioner can include a spring. The tensioner can beconfigured to maintain a tension force of at least one ounce (0.28 N).The tensioner can be configured to maintain a tension force of at leastone ounce (0.28 N) despite thermal expansion of the flexible layeredcircuit structure of up to 1 millimeter per meter in length of theflexible circuit structure. The mounting structure can include afastener. The mounting structure can include a hook. The mountingstructure can include a pin. The mounting structure can include a clip.The mounting structure can include a spring clip. The mounting structurecan include a tab or tab receptacle. The mounting structure can bedirect or indirectly attached to the housing substrate. The flexiblelayered circuit structure can include a first end and a second end,wherein the mounting structure engages the first end and the second end.The flexible layered circuit structure can be in a U shape such that thefirst end and the second end are disposed adjacent to one another. Theflexible layered circuit structure can have a first lateral side and asecond lateral side, wherein the mounting structure can engage at leastone of the first lateral side and the second lateral side. The housingsubstrate can include a material that can be selected from the groupconsisting of organic and inorganic structural materials. The housingsubstrate can include a material that can be selected from the groupconsisting of a polymer, a cellulosic material, a composite, a glass,and stone. The housing substrate can include a metal. The light emittingdiodes mounted on the top layer can have a power of between 0.25 and 3watts per inch squared of the surface area of the bottom layer. Theflexible circuit structure can have sufficient flexibility to achievebending with a radius of curvature of at least 1 inch. The flexiblelayered circuit structure can define apertures, the mounting structurecan be configured to engage the apertures to support the flexiblelayered circuit structure. The bottom thermally conductive layer caninclude a textured surface having a surface area greater than an equallysized substantially flat surface. The bottom thermally conductive layercan include a plurality of heat sink fins mounted thereon. The bottomthermally conductive layer can include a textured surface having asurface area at least 20 percent greater than an equally sizedsubstantially flat surface. The system can further include a coatingover the bottom thermally conductive layer, the coating can include amaterial with properties that enhance heat transfer. The coating caninclude tinning. The bottom layer can be covered with a thermallyconductive and emissive material. The housing substrate can be coatedwith a material to enhance heat flow across the air gap. The top layercan include 0.5 to 4.0 ounces per square foot of copper, theintermediate layer can include fiberglass 0.005 to 0.020 inches thick,and the bottom layer can include 0.5 to 4.0 ounces per square foot ofcopper. The top, intermediate, and bottom layers, together, can have athermal resistance of less than 10 degrees Celsius per Watt. The systemcan be configured to have thermal transfer properties sufficient toallow the system to maintain a thermal equilibrium at or below thecritical junction temperatures for the LEDs without the addition ofsecondary heat sinking. The flexible layered circuit structure isattached to the mounting structure in a releasable manner. The flexiblelayered circuit structure can be releasable from the mounting structurewithout the use of tools. The flexible layered circuit structure can beconfigured for replacement.

In some embodiments, an LED lighting system is included. The LEDlighting system can include a flexible layered circuit structureincluding a top thermally conductive layer, a middle electricallyinsulating layer, a bottom thermally conductive layer, a plurality oflight emitting diodes mounted on the bottom layer, a housing substrate,and a mounting structure. The mounting structure can be configured tosuspend the layered circuit structure above the housing substrate withan air gap disposed in between bottom thermally conductive layer of theflexible layered circuit structure and the housing substrate, whereinthe distance between the layered circuit structure and the support layeris at least about 0.5 mm.

In some embodiments, a method for making an LED lighting system isincluded. The method for making an LED lighting system can includeobtaining a flexible layered circuit structure that includes, a topthermally conductive layer, a middle electrically insulating layer, abottom thermally conductive layer. The method can also includesuspending the flexible layered circuit structure above a housingsubstrate with an air gap disposed in between the bottom thermallyconductive layer of the flexible layered circuit structure and thehousing substrate, wherein the distance between the layered circuitstructure and the housing substrate is at least about 0.5 mm, andconnecting the flexible layered circuit structure to a power source.Suspending can include attaching the flexible layered circuit structureto a mounting structure. The mounting structure can provide theconnection to the power source. The method can further include cuttingthe flexible layered circuit structure to a desired length. The methodcan further include unwinding the flexible layered circuit structurefrom a storage reel prior to cutting. Suspending can include attachingthe flexible layered circuit structure to a mounting structure thatprovides a tension force along the length of the flexible layeredcircuit structure. The method can further include applying a tensionforce of at least one ounce (0.28 N) to the flexible layered circuitstructure. The method can further include removing the flexible layeredcircuit structure from the position suspended above a housing substrate.The step of removing can be accomplished without tools. The method canfurther include replacing the flexible layered circuit structure withanother flexible layered circuit structure.

In some embodiments, a method for operating an LED lighting system isincluded. The method for operating an LED lighting system can includeproviding electrical current to an LED lighting circuit, the LEDlighting circuit including a plurality of light emitting diodes, the LEDlighting circuit disposed upon a flexible layered circuit structure. Theflexible layered circuit structure can include a top thermallyconductive layer, a middle electrically insulating layer, and a bottomthermally conductive layer. The method can further include dissipatingheat from the light emitting diodes to ambient air through the topsurface of the top thermally conductive layer and the bottom surface ofthe bottom thermally conductive layer.

In some embodiments, an LED lighting system is included. The LEDlighting system can include a flexible layered circuit structureincluding a top thermally conductive layer, a middle electricallyinsulating layer, a bottom thermally conductive layer, and a pluralityof light emitting diodes mounted on the top layer. The flexible layeredcircuit structure can be formed into a loop. The loop can be disposedwithin a housing. The loop can be separated from the housing by an airgap. The loop can be disposed sideways to the support structure.

The invention claimed is:
 1. An interconnectable circuit board array,comprising: a first flexible interconnectable circuit board, comprising:a conductive layer between two electrically isolating layers; a firstelectrically conductive pad disposed on a top surface of the firstflexible interconnectable circuit board; a second electricallyconductive pad disposed on the top surface of the first flexibleinterconnectable circuit board; a third electrically conductive paddisposed on the top surface of the first flexible interconnectablecircuit board; a fourth electrically conductive pad disposed on the topsurface of the first flexible interconnectable circuit board; and afirst LED of the first flexible interconnectable circuit board disposedon the top surface, wherein the first LED of the first flexibleinterconnectable circuit board is conductively connected to theconductive layer; and a second flexible interconnectable circuit board,comprising: a conductive layer between two electrically isolatinglayers; a first electrically conductive pad disposed on a top surface ofthe second flexible interconnectable circuit board; a secondelectrically conductive pad disposed on the top surface of the secondflexible interconnectable circuit board; a third electrically conductivepad disposed on the top surface of the second flexible interconnectablecircuit board; a fourth electrically conductive pad disposed on the topsurface of the second flexible interconnectable circuit board; and afirst LED of the second flexible interconnectable circuit board disposedon the top surface, wherein the first LED of the second flexibleinterconnectable circuit board is conductively connected to theconductive layer; wherein the first flexible interconnectable circuitboard is arranged with the second flexible interconnectable circuitboard such that a longitudinal axis of the first flexibleinterconnectable circuit board is aligned with a longitudinal axis ofthe second flexible interconnectable circuit board; and wherein aportion of the first flexible interconnectable circuit board overlaps aportion of the second flexible interconnectable circuit board such thatthe first electrically conductive pad of the first flexibleinterconnectable circuit board is at least partially aligned with thethird electrically conductive pad of the second flexibleinterconnectable circuit board, and the second electrically conductivepad of the first flexible interconnectable circuit board is at leastpartially aligned with the fourth electrically conductive pad of thesecond flexible interconnectable circuit board; wherein the firstelectrically conductive pad of the first flexible interconnectablecircuit board is conductively connected with the third electricallyconductive pad of the second flexible interconnectable circuit board andthe second electrically conductive pad of the first flexibleinterconnectable circuit board is conductively connected with the fourthelectrically conductive pad of the second flexible interconnectablecircuit board; wherein a material is applied to the top surface of thefirst flexible interconnectable circuit board and to the top surface ofthe second flexible interconnectable circuit board, such that thematerial extends over an end of the first flexible interconnectablecircuit board and onto the top surface of the second flexibleinterconnectable circuit board.
 2. The interconnectable circuit boardarray of claim 1, wherein the material is a potting material.
 3. Theinterconnectable circuit board array of claim 1, further comprising athird flexible interconnectable circuit board comprising: a conductivelayer between two electrically isolating layers; a first electricallyconductive pad disposed on a top surface of the third flexibleinterconnectable circuit board; a second electrically conductive paddisposed on the top surface of the third flexible interconnectablecircuit board; a third electrically conductive pad disposed on a topsurface of the third flexible interconnectable circuit board; a fourthelectrically conductive pad disposed on the top surface of the thirdflexible interconnectable circuit board; and a first LED of the thirdflexible interconnectable circuit board disposed on the top surface,wherein the first LED of the third flexible interconnectable circuitboard is conductively connected to the conductive layer; wherein thesecond flexible interconnectable circuit board is arranged with thethird flexible interconnectable circuit board such that the longitudinalaxis of the second flexible interconnectable circuit board is alignedwith a longitudinal axis of the third flexible interconnectable circuitboard; wherein a portion of the second flexible interconnectable circuitboard overlaps a portion of the third flexible interconnectable circuitboard such that the first electrically conductive pad of the secondflexible interconnectable circuit board is at least partially alignedwith the third electrically conductive pad of the third flexibleinterconnectable circuit board, and the second electrically conductivepad of the second flexible interconnectable circuit board is at leastpartially aligned with the fourth electrically conductive pad of thethird flexible interconnectable circuit board; wherein the firstelectrically conductive pad of the second flexible interconnectablecircuit board is conductively connected with the third electricallyconductive pad of the third flexible interconnectable circuit board andthe second electrically conductive pad of the second flexibleinterconnectable circuit board is conductively connected with the fourthelectrically conductive pad of the third flexible interconnectablecircuit board; wherein a material is applied to the top surface of thesecond flexible interconnectable circuit board and to the top surface ofthe third flexible interconnectable circuit board, such that thematerial extends over an end of the second flexible interconnectablecircuit board and onto the top surface of the third flexibleinterconnectable circuit board.
 4. The interconnectable circuit boardarray of claim 1, wherein the interconnectable circuit board array isconfigured to be sufficiently flexible to achieve a radius of curvatureof 6 inches.
 5. The interconnectable circuit board array of claim 1,wherein the interconnectable circuit board array is configured to besufficiently flexible to achieve a radius of curvature of 1 inch.
 6. Theinterconnectable circuit board array of claim 1, wherein theinterconnectable circuit board array is configured to be sufficientlyflexible to be wrapped about a hub of a reel.
 7. The interconnectablecircuit board array of claim 1, wherein the first flexibleinterconnectable circuit board further comprises: a second LED of thefirst flexible interconnectable circuit board disposed on a bottomsurface of the first flexible interconnectable circuit board, whereinthe second LED of the first flexible interconnectable circuit board isconductively connected to the conductive layer.